AN ABSTRACT OF THE DISSERTATION OF

Brennan T. Jordan for the degree of Doctor of Philosophy in Geology presented on June 28, 2001. Title: Basaltic Volcanism and Tectonics of the High Lava Plains, Southeastern Oregon. Redacted for privacy Abstract approved: Redacted for privacy

David W. Graham

The High Lava Plains province (HLP) of southeastern Oregon is a Miocene to Recent volcanic upland characterized by widespread basaltic volcanism and west-migrating rhyolitic volcanism. New 40Ar/39Ar ages for HLP rhyolites demonstrate that the trend of migrating rhyolitic volcanism is robust, reflecting westward migration at a rate of -35 kmlm.y. from 10 to 5 Ma, and -15 km/m.y after 5 Ma. This pattern mirrors the trend of northeastward migrating silicic volcanism of the Snake River Plain to the Yellowstone Plateau. HLP basaltic volcanism was relatively continuous with episodes of heightened activity at -7.6, -5.9, and 2-3 Ma. The 7.6 Ma event coincided with initiation of High Cascades volcanism suggesting a major regional tectonic event. HLP basalts are variably evolved high-alumina olivine tholeiites. Even primitive basalts are enriched relative to mid-ocean ridge basalts (MORB) in incompatible trace-elements, especially Ba, Sr, and Pb. HLP basalts are isotopically evolved relative to MORB with 87Sr/86Sr of 0.70305 to 0.70508 andENdof +6.7 to + 1.6. Isotopic characteristics of Pliocene and Quaternary basalts are more evolved in the east than the west. Miocene basalts are of more uniform isotopic character. Helium isotopes in Quaternary basalts are constant across the HLP with 3He/4He of -9RA,reflecting either a strongly depleted MORB source or interaction with a mantle plume.

The HLP and Snake River Plain are linked by divergent trends of silicic volcanism and a belt of Pliocene and younger basaltic volcanism. To explain both provinces I propose the following. At 17 Ma a small plume head was emplaced under the North American lithosphere, centered near Twin Falls, Idaho, the location predicted by plate tectonic reconstructions. Basaltic volcanism (Columbia River and Steens Basalts) resulted from emplacement of plume head material under thin lithosphere west of the craton margin and from westward flow from the plume up the lithospheric topography at the craton margin. The latter process may also have driven westward mantle flow under the HLP. Westward migrating volcanism of the HLP may also reflect greater times to incubate crustal magmatism further from the center of the plume head. Basaltic Volcanism and Tectonics of the High Lava Plains, Southeastern Oregon

By Brennan T. Jordan

A DISSERTATION

submitted to

Oregon State University

in partial fulfillment of the requirements for the degree of

Doctor of Philosophy

Completed June 28, 2001 Commencement June 2002 Doctor of Philosophy dissertation of Brennan T. Jordan presented on June 28. 2001

APPROVED:

Redacted for privacy

Co-Major Professor, repiQ'senting Geology

Redacted for privacy

Co-Major Professor, representing Geology

Redacted for privacy Head of Department of Gêosciences

Redacted for privacy

Dean of Gpàduàte School

I understand that my dissertation will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my dissertation to any reader upon request.

Redacted for privacy

Brennan T. JorLlan. Author ACKNOWLEDGMENTS

Major funding for the research described in this dissertation was provided by the National Science Foundation by way of a grant to Anita Grunder, Dave

Graham, and Bob Duncan. Additional funding was provided by a Student Research grant from the Geological Society of America. The NSF-RIDGE Program funded my participation in the 2000 Iceland Summer School, which contributed greatly to my perspective on plume processes.

I thank my advisors, Anita Grunder, Dave Graham, and Bob Duncan, for their participation in this research. Particularly, I appreciate their willingness to take one more shot at pursuing grant-support for this research. I thank Anita for her deep involvement in this project, her critical consideration of the problems posed by High Lava Plains magmatism, and her attempts to keep me on the petrologic straight and narrow. Dave and Bob offered analytical assistance and intellectual contributions well beyond the budgeted support for this project. I also thank Gene

Humphreys of the University of Oregon for sharing his ideas on geologic processes of the western United States.

Many aspects of my research and studies at Oregon State University benefited from interactions with other faculty in the Department of Geosciences and the College of Oceanic and Atmospheric Sciences, notably, Ed Taylor, Dave

Christie, Roger Nielsen, and Andy Ungerer. Special thanks to Lew Hogan and John

Huard for their help in the argon geochronology lab.

I thank my colleagues at Southern Oregon University, Monty Elliott, Jad

D'Allura, Eric Dittmer, Charles Lane, and Joe Graff, for friendship while I taught at

SOU and for their unwavering insistence that progress be made on this document while I was there.

I also wish to thank the professors who shepherded me though my earlier phases of education in geology: Charles Merguerian (Hofstra University), Karl

Karistrom (Northern Arizona), Dave Rodgers (Idaho State University), and Paul

Link (Idaho State University). I reflect upon my experiences with them frequently, and am very grateful for their contributions.

Lastly, I acknowledge the support of my family. My mother, father, and grandmother strongly supported this endeavor and offered critical financial assistance when needed. I thank my wife, Jeanne, and stepchildren, Caleb and

Justine, for their love, support, and patience while I have pursued this degree. CONTRIBUTION OF AUTHORS

Anita Grunder, David Graham, Bob Duncan, Alan Demo (Berkeley

Geochronology Center), and Bruce Nelson (University of Washington) are listed as co-authors for the manuscripts submitted as chapters 2, 3, and 4 of this dissertation.

Grunder collected a significant number of the samples analyzed in this study (those with sample number format HLP-98-##), and assisted in the selection of samples for geochemical and geochronologic analysis. Grunder and her former students

Martin Streck, Jim MacLean, and Jenda Johnson collected all of the samples analyzed by 40Ar/39Ar at the Berkeley Geochronology Center. Graham assisted in sample selection for helium isotope analysis, and performed these analyses.

Duncan assisted in performing 40Ar/39Ar analyses at Oregon State University and in the interpretation of these results. Demo performed 40Ar/39Ar analyses conducted at the Berkeley Geochronology Center and interpreted the results of these analyses. Nelson performed strontium, neodymium, and lead isotope analyses. Grunder, Graham, and Duncan provided critical reviews of the three manuscripts constituting chapters 2,3, and 4 and suggested substantive revisions. TABLE OF CONTENTS

Chapter 1: Introduction to the Problem of High Lava Plains Magma Genesis .1

The High Lava Plains volcanic field...... 1

Rhyolites of the High Lava Plains...... 5 Basalts of the High Lava Plains...... 6 Structural Geology of the High Lava Plains and Adjacent Northern Basin and Range...... 7

Models for High Lava Plains Magmatism...... 10

Propagating Rifts or Shear Zones...... 10 Plume Head Entrainment...... 11 Evolving Back Arc Extension...... 14

Introduction to Following Chapters...... 16

Chapter 2: Geochronology of Oregon High Lava Plains Volcanism: Mirror Image of the Yellowstone Hotspot?...... 17 Abstract...... 18

Introduction...... 19

The High Lava Plains...... 22

VolcanicRocks...... 22 Sturcture...... 23 Previous Geochronology...... 24

Methods...... 25

Berkeley Geochronology Center...... 26 Oregon State University...... 27

Results...... 27 TABLE OF CONTENTS (CONTINUED)

Discussion......

Propagation of Rhyolitic Volcanism...... 37 Middle Miocene Silicic Volcanism...... 41 Comparison of the HLP and YSRP trends...... 45 Cause of Migrating Volcanism of the HLP...... 48

Conclusions...... 55

Acknowledgments...... 56

ReferencesCited...... 57

Chapter 3: Helium Isotope Composition of Basalts of the Oregon High Lava Plains: Bearing on Relationship to Yellowstone-Snake River Plain Magmatism...... 63 Abstract...... 64

Introduction...... 65

Basalts of the High Lava Plains...... 69

Methods...... 70

Results...... 70

Interpretation of Marginal Results...... 74 High Lava Plains Helium Isotope Composition: Summary...... 75

Origin of High Lava Plains Helium Signal...... 77

Implications for Genesis of the High Lava Plains and Relationship to the Yellowstone-Snake River Plain System...... 80

Conclusions...... 83

References Cited...... 84 TABLE OF CONTENTS (CONTINUED)

Chapter 4: Basaltic Volcanism of the Oregon High Lava Plains...... 90

Abstract...... 91

Introduction...... 92

TectonicSetting...... 93 PreviousStudies...... 97

Methods...... 100

Results...... 102

Occurrence...... 102 Petrography ...... 102 Major Element Composition...... 103 Trace Element Composition...... 112 IsotopicComposition ...... 116 Spatial and Temporal Variation in HLP Basalt Composition...... 121

Genesis of the High Lava Plains Basalts...... 125

Source of Basaltic Magmas...... 125 Evolution of Basaltic Magmas...... 131

Summary Petrologic Model for Genesis of High Lava Plains Basaltic Magmas...... 137

ReferencesCited...... 141

Chapter5: Summary...... 149

Conclusions...... 149

Problems for Further Study...... 150 TABLE OF CONTENTS (CONTINUED)

Bibliography...... 152

Appendices ...... 165

Appendix 1: Major and Trace Element Analyses of High Lava Plains Basalts ...... 165

Appendix 2: Major and Trace Element Analyses of Non-Basalts ...... 181

Appendix 3: Detailed Data for 40Ar/39Ar Analyses Conducted at Oregon State University ...... 182 LIST OF FIGURES

Figure Eag

1.1 Physiographic provinces of Oregon (after Dicken, 1950), WV=Willamette Valley ...... 2

1.2 Panoramic view of the western High Lava Plains looking northfrom GreenMountain ...... 3

1.3 Tectonic setting of the High Lava Plains ...... 4

1.4 Distribution of rhyolites, and isochrons depicting ageprogression of rhyolites of the HLP (after MacLeod and others, 1975) ...... 5

1.5 Faults of the High Lava Plains and nothwestern Basin andRange of southeastern Oregon (after Walker and MacLeod, 1991) ...... 8

1.6 Shaded digital relief map of the Snake River Plain,Yellowstone Plateau, and surroundings showing hotspot tracks predicted for 17million years working back from Yellowstone (YS) based on global platemotion models plus 20% extension in the direction of propagation(Rodgers and others, 1994) ...... 12

2.1 Map showing the tectonic setting of the Oregon HighLava Plains and SnakeRiver Plain ...... 20

2.2 Map of faults of the High Lava Plains andnorthwestern Basin and Range after Walker and MacLeod (1991) ...... 24

2.3 Maps of the High Lava Plains showing thedistribution of (A) rhyolites and(B) basalts ...... 32

2.4 Age-probability spectra for all samples dated bythe laser total-fusion method ...... 34

2.5 Age probability diagrams for auxiliary plots of40Ar /39Ar analytical data (moles 39Ar, percent radiogenic40Ar [40Ar*1,Ca/K ratio, and a display of individual analyses) for laser total-fusiondating of coexisting obsidian glass and sanidine from sample HP-91-10collected from Horse Mountain .....35 LIST OF FIGURES (CONTINUED)

Page Figir

2.6 Representative plateau and inverseisochron plots for incrementalheating 36 analyses performed at Oregon StateUniversity ......

2.7 Plot of previous and new rhyoliteand basalt ages versusdistance along the 39 HLPtrend ...... 43 2.8 Statistical plots of previousand new ages for HILP basalts ......

2.9 Cartoon depicting the scenarioenvisioned to explain thedistribution of Middle Miocene basaltic vents, andtrends of migrating silicicvolcanism 52 ofthe HLP and YSRP ...... isotope determinations in the western 3.1 Map showing previous helium 67 UnitedStates ...... determinations from 3.2 Map of the High Lava Plainsshowing helium isotope 71 thisstudy ...... longitude ...... 76 3.3 Plot of helium isotope determinations(±1c uncertainty) versus

3.4 Map showing the extent of asymmetric Yellowstone plumehead with a radius of 650 km at the time ofemplacement (-'17 Ma) (toreach across the lithosphere HLP and to Medicine Lake Volcano),and regions of different 82 and extensional history relevant tosubsequent magma genesis ......

setting of the Oregon HighLava Plains and 4.1 Map showing the tectonic 94 SnakeRiver Plain ......

the High Lava Plainsprovince, after 4.2 Age and distribution of basalts of 98 Jordan and others, in prep. (Chapter2) ...... 107 4.3 Classification plots of HLPbasalts ...... MgO of HILP 4.4 Plots of major elementconcentration and CaO/A1203 versus 110 basalts ...... 111 4.5 Additional major elementvariation plots ...... LIST OF FIGURES (CONTINUED)

Figure

4,6 Trace elements plotted against MgO ...... 113

4.7 Field of trace element composition ofFILP basalts presented in MORB- normalized incompatible-element spider diagram(A), and a MORB- normalized rare-earth element diagram (B) ...... 114

4.8 Plots of isotopic ratios of HLP basalts ...... 118

4.9 Variation in isotopic ratios with majorand trace element composition ...... 120

4.10 Sr and Nd isotopic variation withlongitude and age ...... 122

4.11 Variation in selected trace elementratios of the set of 42 primitivebasalts withlongitude ...... 123

4.12 Trace element ratio plots constructed toexplore the relative significance of different contributions to the mantle sourceand the role of varying degrees of partial melting in the genesisof primitive HLP basaltic 128 magmas ......

4.13 Plot of Sc versus CaO/A1203 ofHLP basalts ...... 132

4.14 Results of three MELTS (Ghiorsoand Sack, 1995) runs that are consistent with, or bound, most of the datafor HLP basalts ...... 134

4.15 Cartoon depicting the scenarioenvisioned to explain thedistribution of Middle Miocene basaltic vents, andtrends of migrating silicicvolôanism of the HLP and YSRP ...... 139 LIST OF TABLES

Table Page

2.1 Summary of Single-Grain Laser Total-Fusion 40Ar/39Ar Results...... 29

2.2 Summary of Incremental-Heating 40Ar/39Ar Results from Berkeley Geochronology Center...... 29

2.3 Summary of Incremental-Heating 40Ar/39Ar Results from Oregon State University...... 30

3.1 Helium Isotope Determinations...... 71

3.2 Major and Trace Element Composition of Successfully Analyzed Samples ..... 73

4.1 Average and Representative HLP Basalt Compositions...... 104

4.2 Isotopic Analyses...... 117 This dissertation is dedicated to the memories of my grandmother Liz Davison and father-in-law Ted Fromm. Both were strongly supportive of my pursuit of this degree but did not live to see it through. Both contributed greatly to my perception of beauty and wonder in our world. BASALTIC VOLCANISM AND TECTONICS OF THE HIGH LAVA PLAINS, SOUTHEASTERN OREGON

CHAPTER 1: INTRODUCTION TO THE PROBLEM OF HIGH LAVA PLAINS MAGMA GENESIS

In this chapter I provide a general introduction to the problems posed by

High Lava Plains volcanism, review the regional setting, and evaluate previous hypotheses for the tectonic processes responsible for genesis of High Lava Plains magmas. The subsequent chapters are manuscripts to be submitted for publication.

As such, there is some redundancy in the introductory sections of those chapters.

However, this chapter will include a more thorough discussion of some aspects of regional geology including the structural geology.

THE HIGH LAVA PLAINS VOLCANIC FIELD

The High Lava Plains physiographic province (HLP) is a volcanic upland extending 275 km east-west and 85 km north-south across central and southeastern

Oregon (Dicken, 1950; Fig. 1.1). Volcanic rocks exposed in the HLP are predominantly Middle Miocene and younger basalt lava flows and cinder cones, and rhyolite domes and ash-flow tuffs, with intercalated tuffaceous and volcaniclastic sedimentary rocks (Walker and Repenning, 1965; Walker and others,

1967; Greene and others, 1972; MacLeod and Sherrod, 1992; MacLeod and others,

1995). Petrologically significant, but volumetrically minor, intermediate volcanic 2

123° 121° 119° 117°

100 km 46°

Columbia Plateau

I 44°

HighLavap

IPlateau

Basin and Range Kiamath 42° Mountains

Figure 1.1 Physiographic provinces of Oregon (after Dicken, 1950), WV Willamette Valley.

rocks are also present (e.g. MacLean, 1994; Johnson and Grunder, 2000). Walker

(1974) and MacLeod and others (1975) documented that silicic volcanic rocks of

the HLP are progressively younger from -40 Ma in the east to <1 Ma in the west.

Westward propagating silicic volcanism, and bimodal volcanism, also occur in the northernmost -100 km of the Basin and Range province immediately south of the

HLP (Walker, 1974; MacLeod and others, 1975).

Prior to the current study, the geochronologic data set for HLP silicic

volcanic rocks consisted of 45 K-Ar ages and one 40Ar/39Ar age through which a 3

Figure 1.2 Panoramic view of the western High Lava Plains looking north from Green Mountain. Bimodal volcanism of the HLP is represented by rhyolite domes (China Hat, East Butte, Quartz Mountain, Frederick Butte, and Hampton Butte), basalt cinder cones (Fox Butte, Lava Mountain, and Walker Butte), anda small basaltic shield (East Lava Field).

reasonably consistent set of isochrons could be drawn depicting westward

progression of silicic volcanism (Fig. 1.3). The pattern of isochrons suggested

migration of volcanism as a wave as opposed to a migrating point source. At any

longitude volcanism is older in the northwestern Basin and Range than the HLP at

any given longitude, creating a set of generally NE trending isochrons. The

isochrons are not perfectly linear, but rather are sometimes curved or irregular, becoming more complex with decreasing age. These complications do not negate

the significance of the trend, and may, in fact, be important in understanding the genesis of the volcanic trend.

The tectonic processes responsible for the genesis of the HLP volcanic field are poorly understood. Particularly hard to explain is the west-younging pattern of silicic volcanism. Previously proposed hypotheses ascribe enigmatic HLP magmatism to: 1) propagation of shear zones accommodating the northward 4

-f4o 13O 125 120° 115° 110

Figure 1.3. Tectonic setting of the High Lava Plains. Y=Yellowstone, NV=Newberry Volcano, M=McDermitt Caldera. Pliocene and younger basalts of the HLP and Snake River Plain are shaded orange. The bold dash-dot line shows the limit of Basin and Range extension. Curved lines cutting across the IILP and northwestern Basin and range are isochrons of silicic volcanism, 10 Ma and 1 Ma are labeled. Encircled areas are caldera complexes of the Snake River Plain and the Owyhee region (after Pierce and Morgan, 1992); ages are given for some calderas to indicate age progression. Also shown are dike complexes which fed Middle Miocene flood basalts; CRB, Columbia River basalt dikes; SB, Steens Basalt dikes; NNR, Northern Nevada Rift. The light dashed lines indicate approximate positions of the Sr-isotope discontinuities (after synthesis of Ernst, 1988); the 0.706 line is thought to broadly delineate the craton margin.

decline in extension (Christiansen and McKee, 1978; Christiansen, 1993); 2) an evolving subduction geometry and associated extension (Carlson and Hart, 1987);

3) westward advection of a portion of the Yellowstone plume system by subduction induced mantle flow (Draper, 1991); and 4) ascent of asthenosphere as it flowed around the buoyant residuum of voluminous Middle Miocene magmatism in a 122 121 12O 119 118

44

China 5. -.Quartz Burns Mountain Glass Juniper Butte Newberry Butte Ridge Volcano .451.

Duck' 43 Butte -1 Mount 50Km

4 Butte

I Quartz Butte

42 Rhyolite Domes lsochrons (Ma) showing progression silicic volcanism

Figure 1.4 Distribution of rhyolites, and isochrons depicting age progression of rhyolites of the HLP (after MacLeod and others, 1975)

flow-field induced by subduction (Humphreys and others, 2000). The purpose of the research described in the following chapters was to resolve the tectonic processes responsible for HLP magmatism. The approach taken to this problem was to study basalts of the HLP to document the variation in time and space of mantle processes, and to synthesize these interpretations with previous petrologic studies of HLP rhyolites.

Rhyolites of the High Lava Plains

Rhyolites of the HLP were erupted as domes and dome complexes, with significant tuffs erupted at 9.7 Ma (Devine Canyon tuft'), 8.5 Ma (Prater Creek tuft), and 7.1 Ma (Rattlesnake tuft) and lesser tuffs emplaced subsequently. Silicic rocks of the HLP are generally metaluminous and vary from low-silica to high- silica rhyolites. Low-silica rhyolites are interpreted to be the product of 10-30% partial melting of the middle or lower crust, and high-silica rhyolites are interpreted to reflect fractional crystallization of low-silica rhyolites (Grunder, 1992, MacLean,

1994; Streck and others, 1999; Johnson and Grunder, 2000).

Basalts of the High Lava Plains

A progression of age of initiation of basaltic volcanism is suggested by the observation that of 47 previously dated basalts, only three are more than two million years older than rhyolites in the same area. However, this may reflect a sampling bias due to subsequent cover and limited erosional incision of older rocks in the west. Basalts of the HLP have been the primary focus of study of Draper

(1991). In broader regional studies, Hart and others (1984) and Hart (1995) recognized the predominance of high-alumina olivine tholeiites (HAOT) among basalts of the HLP and northwestern Basin and Range. HAOT are also a component of volcanism in the Cascade Range and Columbia Plateau (Bailey and

Conrey, 1992).

HLP basalts, and HAOT in the adjacent provinces, are characterized as similar to mid-ocean ridge basalts (MORB) in major element composition, but substantially enriched relative to MORB in incompatible trace elements (McKee and other, 1983; Hart and others, 1984; Draper, 1991). McKee and others (1983) and Hart and others (1984) also noted the similarity between HAOT and back arc 7

basin basalts (BABB); however, HLP basalts have higher Ba and Sr concentrations and lower K/Ba than either MORB or BABB. Rare earth element patterns of HLP basalts are similar to BABB (McKee and others, 1983). The compositional similarity to MORB suggests a similar origin, by partial melting of depleted mantle at relatively shallow depths. Bartels and others (1991) performed experimental studies with a primitive HAOT from Medicine Lake Volcano, and found it to be in equilibrium with a mantle mineral assemblage of olivine, orthopyroxene, clinopyroxene, plagioclase, and spine! at 11 kb.

Structural Geology of the High Lava Plains and Adjacent Northern Basin and

Range

The structural geology of the HLP is dominated by two patterns: the

Brothers fault zone and Basin and Range faulting (Fig. 1.4). The Brothers fault zone is a set of northwest trending faults that cuts obliquely the HLP (Lawrence,

1976). The faults of the Brothers fault zone are recognized by relatively continuous

(typically 5-20 km) fault scarps of modest relief (generally <100 m), commonly occurring in en echelon groups (Walker, 1969; Lawrence, 1976). Lawrence (1976) interpreted the Brothers fault zone to be one of several dextral shear zones which accommodate the northward termination in Basin and Range extension. The areas separating Lawrence's (1976) fault zones are areas of subsequent cover, so it seems more appropriate to consider them one continuous fault zone. Clayton (1989) 11W 11<

\\ \-

\'l N (1 \ \\\ \ 0 7/ /"\ HB \ ;\\'k\\ _y\j' 0. -

43 ) /

II'

Hh La Pields km Baser and Range L. Faults <3Com Topographic Relief I Faults >30Cm Topographic Rebel

Figure 1.5. Faults of the High Lava Plains and nothwestern Basin and Range of southeastern Oregon (after Walker and MacLeod, 1991). WR=Winter Rim, AR=Abert Rim, PJ=Poker Jim Ridge, SM=Steens Mountain, NC=Newberry Caldera, and HB=Harney Basin.

supported the interpretation of right-lateral shear in the Brothers faultzone while noting that actual displacement on faults is almost completely normal. Donath

(1962) interpreted conjugate fault patternsas reflecting both right-lateral and left- lateral shear. Pezzopane and Weldon (1993) observed a concentration of active

(Holocene) faults in ,and south of, the western HLP including NNE-trending Basin and Range faults (e.g. Abert Rim and Winter Ridge) and NW-trending faults (e.g.

Crack-in-the-Ground and Paulina Marsh fault). They and Hemphill-Haley (1999) interpret this belt of active faulting to link up with the Cascades to the north and

Walker Lane to the south in a zone accommodating extension and dextral shear at the North American plate margin. They do not recognizeany evidence for

Holocene activity in the Brothers fault zone in the centralor eastern HLP.

Basin and Range faults generally trend north-northeast, and decline substantially in apparent offset in the northwestern Basin and Range immediately south of the HLP (Fig. 1.4). The northward decline in offset eliminates the requirement that the Brothers fault zone be a major accommodation zone. Basin and Range faults in southeastern Oregon are steep, widely spaced, and, with the exception of Steens Mountain, of generally modest (<2,000 m) apparent offset, generating relatively minor tilts within fault blocks. This pattern is typical of regions of relatively minor extension (Stewart, 1998).

By measuring fault scarp heights on several transects across the southeastern Oregon Basin and Range (west of Steens Mountain), and assuming reasonable dip angles (-.75°) and basin fill (50% of exposed scarp height for major faults with no apparent bedrock in the basin), I estimate that Miocene andyounger extension declines from -4% to -1% in the 100 km south of the HLP. The magnitude of extension accommodated by faults within the HLP appears to be quite minor. Based on the examination of the cross sections of Sherrod and Johnson

(1994), in an area reasonably representative of the HLP mapped at 1:24,000 scale, I estimate -1% WNW-ESE extension on Basin and Range faults, and -1% NE-SW extension of Brothers faults since 7 Ma. 10

MODELS OF HIGH LAVA PLAINS MAGMATISM

Propagating Rifts or Shear Zones

The symmetry and co-origination of the HLP and Yellowstone-Snake River

Plain (YSRP) trends, and the positions of these trends at, or near, the northern margin of the extending Basin and Range province, has given rise to the hypothesis that these trends reflect propagating rifts or shear zones (Smith, 1977; Chnstiansen and McKee, 1978; Christiansen, 1993). This hypothesis is supported by the overlap between the HLP with the Brothers fault zone.

Smith (1977) envisioned three rifts, the YSRP, HLP, and the Northern

Nevada Rift, propagating at 120° to one another, with magmatism presumably being driven by decompression melting of upwelling mantle in areas of extension.

This model is no longer considered viable because it requires that extension be directed perpendicular to the trends (e.g. Smith and Braille, 1994).

Christiansen and McKee (1978) and Christiansen (1993) proposed that magmatism of the YSRP and HLP trends reflects melting driven by basal lithosphenc shear occurring at the tips of propagating shear zones enhanced by a dynamic feedback mechanism. They considered the HLP and YSRP to coincide with significant shear zones that accommodate the northward termination of Basin and Range extension with dextral and sinistral shear, respectively. There is no evidence for lateral shear in, or adjacent to, the Snake River Plain, and there is no significant change in Miocene and younger extension north and south of the plain 11

to require accommodation, so this model does not seem appropriate for the YSRP trend. The coincidence between the HLP and the Brothers faultzone makes this model more appropriate for the HLP trend. It is difficult to explain mantle melting without the addition of heat because the magnitude of extension isso low. Johnson

(1995) and Streck and others (1999) suggested that the HLP trend might be caused by the westward propagation of Basin and Range extension, and that Quaternary basaltic volcanism is the equivalent of leaky transform faults of theocean basins, although these are also areas of localized high extension. Given the low magnitudes of extension involved an additional heat sourceor cause of upwelling must be present.

Plume Head Entrainment

The Yellowstone-Snake River Plain trend is widely interpreted as the result on the southwestward motion of the North American plate over a stationary mantle plume (e.g. Pierce and Morgan, 1992; Smith and Braile, 1994). Volcanism producing the Columbia River basalts is has been interpreted as reflecting the

"plume head" phase of this mantle plume (e.g. Dodson and others, 1997). There are problems with a simple mantle plume interpretation of the YSRP trend including: difficulty in explaining the apparently related HLP trend; disjunct between the trend and the Columbia River basalt vents; and the misfit between the track length

(to McDermitt caldera at -16 Ma) and global plate motion models (Fig. 1.5). ode! Referneces others, 1993 d Richards, 1 991 Gordon, 1 990 Gordon and Jurdy, 1 986 Engebretson and others, 1 985 - * -Gripp and Gordon, modified to consider 1 0 Ma of bending of plume and motion of plume 0'after ConneIL2000j Steinberger and

Figure 1 .6. Shaded digital relief map of the Snake River Plain, Yellowstone Plateau, and surroundings showing hotspot tracks predicted for 17 million years working back from Yellowston (YS) based on global plate motion models plus 20% extension in the direction of propagation (Rodgers and others, 1994). In none of the models does the predicted track reach McDermitt Caldera (MC), the point generally cited as the initiation point of the trend (e.g. Smith and Braile, 1994). 13

In the context of a mantle plume origin for the YSRP trend, Draper (1991)

proposed a model linking the two trends within the plume context. He proposed

that the HLP trend reflects the entrainment of a portion of the head of the YSRP

plume in the subduction-induced asthenopheric counterfiow in the mantle wedge

above the subducting Juan de Fuca plate. This mechanism providesa well-defined

source of heat and a potentially testable source of material contribution to

magmatism. However, it is inconsistent with the current understanding of plume

head dynamics in which a plume heads a plume head undergoes most of its

flattening prior to its impact with the base of the lithosphere (Griffiths and

Campbell, 1991).

Humphreys and others (2000) proposed a related model that could potentiallyexplain both the HLP and YSRP trends without invoking a mantle

plume. In this model the buoyant mantle residuum of Columbia River basalt and

Steens Basalt magmatism was attached to the base of the lithosphere, and mantle

flowing along its base, either to the east due to plate motion (YSRP) or the west

due to subduction induced counterfiow (HLP) rose at its margins, and

decompressed leading to partial melting. One apparent problem with this model is

that the HLP propagates westward from the site of the Steens Basalt eruption, and

no such phenomenon propagates from the site of the eruption of the more

voluminous Columbia River basalt. 14

Evolving Back Arc Extension

The HLP lies in a back arc position with respect to the Cascadearc (1.1).

The back arc regions of subductionzones are often characterized by extension and distinctive, 'MORB-like' magmatism. This is most well defined inareas where the back arc region is underlain by oceanic lithosphere. In theseareas, formation of new oceanic-type lithosphere occurs at a spreading center, somewhat analogous to a mid-ocean ridge. Back-arc phenomena are not as well characterized in areas where the back arc occurs in an area of continental lithosphere. Scholz and others

(1971) and Eaton (1984) related extension in the Basin and Range province to back-arc subduction-related processes, though this interpretation is not currently regarded as valid (e.g. Sonder and Jones, 1999).

Based on the above BABB-like characteristics of HLP basalts described above, Carlson and Hart (1987) proposeda detailed model explaining the

Steens/CRB magmatic event and subsequent tholeiitic volcanism in the back-arc context. In this model, at 18-14 Ma asthenospheric flow was focused at the margin of the Wyoming craton, and rapid ascent of asthenospheric material led to the generation of large volumes of melt, some of which was erupted as the CRB and

Steens Basalt. Following this event, from 10 Ma to present, considerable extension occurred in the back arc region causing melting to occur in the mantle lithosphere which had been depleted by the previous magmatic event. Silicic magmatism is interpreted to mark the westward extent of this region of back arc magmatism through time. 15

Several considerations make this model problematic. First, it hasnot been

demonstrated that significant changes in the geometry of the subducting slab have

occurred on the relevant time scale. Priest (1990) inferred changes in thegeometry

of the slab based on changes in the focus of Cascade volcanism, but the

spatial/temporal patterns of older Cascade volcanic rocksare controlled largely by

eastward tilting of the Western Cascadesequence (Verplanck and Duncan, 1987).

Another consideration is that, at the time this modelwas published, rotation of the

Coast Range, documented by paleomagnetic studies,was widely attributed to

extension in the HLP and northern Basin and Range (e.g. Magill and Cox, 1980).

Wells and Heller (1988) presented a modelmore consistent with HLP and Basin

and Range geology in which some rotation is by internal deformation of the Coast

Range. Lastly, the time frame of Columbia River basalt magmatismwas very brief

(Imnaha and Grande Ronde Basalts constituting 90% by volumewere erupted

between 17.2 and 15.6 Ma; Hooper and Hawkesworth, 1993), which doesnot fit

with asthenospheric upwelling stimulated by extension alone (i.e. withouta mantle plume).

In the preceding discussion I have presented concerns with all of the models previously proposed to explain migrating silicic volcanism of the HLP. However, these models represent the only efforts to explain this phenomenon, andwere considered as the best working hypotheses as I initiated this research. I also considered the possibility that selected aspects of several models might, in combination, be responsible for the HLP trend. Iri

INTRODUCTION TO FOLLOWING CHAPTERS

In the following chapters I describe the results of differentavenues of research undertaken to try to documentprocesses responsible for HLP magmatism.

The preexisting geochronologic framework for the HLP volcanism consisted almost entirely of K-Ar ages with limited precision and unassessable impact of excess argon and argon loss. Chapter 2 presents53new 40Ar/39Ar ages on basalts and rhyolites. Helium isotopes potentially offer the best possible geochemical test for a link between YSRP and HLP basaltic volcanism because basalts of the YSRP have distinctly elevated 3He/4He ratios; Chapter 3 presents helium isotope data for

HLP basalts. Numerous major element and trace element analyseswere made for

HLP basalts, as well as a limited number of Sr, Nd, and Pb isotopic analyses. The results and interpretation of these analyses are presented in Chapter 4. Chapter5 offers a brief summary of the significant conclusions of the preceding chapters. 17

CHAPTER 2

GEOCHRONOLOGY OF OREGON HIGH LAVA PLAINS VOLCANISM: MIRROR IMAGE OF THE YELLOWSTONE HOTSPOT?

Brennan T.Jordan1

Anita L.Grundert

Robert A.Duncan2

Alan L.Demo3

1Department of Geosciences, Oregon State University, Corvallis, OR 97331

2College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331

3Berkeley Geochronology Center, 2455 Ridge Rd., Berkeley, CA 94709

for submission to JournalofVolcanology and Geothermal Research ABSTRACT

The High Lava Plains province (HLP) isa late Cenozoic bimodal volcanic

field at the northern margin of the Basin and Range province in central and

southeastern Oregon. The HLP is characterized by widespread basaltic volcanism

and age-progressive rhyolitic volcanism. We present 40Ar/39Ar laser total-fusion,

laser incremental heating, and furnace incremental heatingages for 19 rhyolite

domes, 5 rhyolite ash-flow tuffs, and 32 basaltic lavas from the HLP. The trend of

migration of HLP rhyolites is confirmed, with propagation west from Duck Creek

Butte (10.4 Ma) to the Newberry Volcanoarea (<1 Ma). The rate of propagation is

35 kmlm.y. from 10 to 5 Ma, slowing to 14 kmlm.y. after 5 Ma. Three dacite

domes, Little Juniper Mountain, Horsehead Mountain, and Jackass Butte, yielded

ages of 15.5 Ma. These domes are part of a regional Middle Miocene intermediate

to silicic volcanic event in northwestern Nevada and southeastern Oregon. Ages for

HLP basalts varied from 138 ka to 10.4 Ma. Statistical analysis ofnew and previous basalt ages suggests that while basaltic volcanismwas essentially continuous across the HLP since 10 Ma, therewere several episodes of increased activity at approximately 7.6, 5.9, and 2-3 Ma. The 7.6 Ma episodewas the most robust, and corresponds with the initiation of High Cascade volcanism suggesting that they are related to a regional tectonic event.

The trend of migrating silicic volcanism crudely mirrors the northeast propagation of the Yellowstone-Snake River Plain system (YSRP), with both trends emerging from the axis of Middle Miocene basaltic volcanism of the 19

Columbia River and Steens basalts. The provinces are further relatedas they

constitute a relatively continuous belt of Pliocene and younger volcanism. We

propose a model which explains both trends and the Middle Miocene large igneous

province as the consequences of interactions between a mantle plume and the

structurally complex North American lithosphere: the Middle Miocene event

reflects emplacement of a plume head 1000 km in diameter, which underwent

melting only where emplaced under thin lithosphere west of the craton margin; the

HLP trend is the result of increased lag times required to incubate crustal

magmatism further from the center of the plume head; and the YSRP trend is the

result of the motion of the North American plate over the plume stem.

INTRODUCTION

The High Lava Plains province (HLP) of central and southeastern Oregon is

a Late Tertiary to Quaternary bimodal volcanic field. Silicic volcanic rocks of the

HLP are progressively younger to the west (Walker, 1974; MacLeod and others,

1975; McKee and others, 1976), mirroring the northeastward progression of silicic

volcanic centers of the Snake River Plain to the Yellowstone Plateau (Armstrong

and others, 1975). Migrating volcanism of the Yellowstone-Snake River Plain

magmatic system (YSRP) is widely interpreted as the trace of a mantle plume now

under Yellowstone. The existence of the antithetic HLP trend is often cited as evidence against this hypothesis (e.g. Christiansen and McKee, 1978; Hamilton,

1989; Christiansen, 1993). Proponents of the plume interpretation note differences 20

A

A I I AA -, l \ CAB i4/ A )i I 45 Iii i'll A /1'N.....'° / HighLava /.//1 Plains

if Aj MO NNR\ ? Ii 100km 40 130° 125° 120° 115° 110°

Figure 2.1. Map showing the tectonic setting of the Oregon High Lava Plains and Snake River Plain. Y=Yellowstone, NV=Newberry Volcano, M=McDermitt Caldera. Pliocene and younger basalts of the HLP and YSRPare shaded gray. The bold dash-dot line shows the limit of Basin and Range extension. Curved lines cutting across the HLP and northwestern Basin and Rangeare isochrons of silicic volcanism, 10 Ma and 1 Ma are labeled. Encircled areasare caldera complexes of the YSRP and Owyhee region (after Pierce and Morgan, 1992);ages are given for some calderas to indicate age progression. Also shown are dike complexes which fed Middle Miocene flood basalts; CRB, Columbia River basalt dikes; SB, Steens Basalt dikes; NNR, Northern Nevada Rift. Striped lines across the YSRPare back- projected from Yellowstone to show the lengths of hotspot tracks predicted by global plate motion models (the northern line is based on Gripp and Gordon, 1990; the southern line is based on Duncan and Richards, 1991). The light dashed lines indicate approximate positions of the Sr-isotope discontinuities (after synthesis of Ernst, 1988); the 0.706 line is thought to broadly delineate the craton margin. 21

between the trends and suggest that theyare not linked (Pierce and Morgan, 1992),

or that the HLP trend may not be a robust feature (Smith and Braile, 1994).

We view three lines of evidenceas supporting a link between the HLP and

YSRP trends. First, both trends emerge froma broad region of intermediate to

silicic volcanism that began with and continued after the eruption of flood basalts

(Columbia River basalts, Steens Basalts, and Northern Nevada Rift volcanism)

along an axis which splits the trends (Fig. 2.1). Also, both trends became well-

defined at about 11 Ma, and migrated at similar rates from that timeto the present.

Finally, Quaternary basalts are found along the lengths of both trends, and in the

intervening Owyhee Plateau.

The HLP separates the Basin andrange extensional province from the less

extended Blue Mountain province to the north; and to the west the HLP impinges

upon the Cascade Range (Fig. 2.1). Previous models relate the HLP trend to one or

more of the processes active in the adjacent provinces. Christiansen (1993)

proposed that the HLP trend is the result ofa propagating shear zone

accommodating the northward termination of Basin and Range extension. Carlson and Hart (1987) related Middle Miocene magmatism and subsequent propagation of HLP silicic volcanism to the backarc setting, and a change in the geometry of subduction. Draper (1991) proposed that the HILP trend reflects the entrainment of plume head material in a subduction induced asthenospheric counter flow cell.

Humphreys and others (2000) refined this model, proposing that both the HLP and

YSRP trends could result from mantle flow around the buoyant residuum of Middle 22

Miocene magmatism (without speculating about the origin of this magmatism) in

the shear fields created by plate motion and counter flow.

The problem of complex patterns of migrating volcanism posed by the HLP

and YSRP trends has been recognizedas one of the outstanding puzzles in

understanding volcanism in the Pacific Northwest (Swanson,1982;Lipman,1992).

We present here new 40Ar/39Ar incremental heatingages for rhyolites and basalts

of the HLP and consider the bearing of theseages on the origin of the HLP trend

and the potential relationship between the HLP and YSRP trends.

THE HIGH LAVA PLAINS

Volcanic Rocks

The HLP is underlain by widespread, thin lava flows of basalt intercalated

with rhyolitic ash-flow tuffs and tuffaceous sediments and punctuated by rhyolite

dome complexes. Basalts are mostly tholeiites (the high-alumina olivine tholeiites

of Hart and others,1984),though basaltic andesites, some calc-alkaline, constitute

approximately a quarter of analyzed mafic samples (Chapter 4). HLP basaltsare

generally aphanitic to sparsely porphyritic with plagioclase (up to 1 cm) and olivine

(up to 3 mm) being common phenocrysts. Clinopyroxene phenocrysts occur in

some evolved basalts. Glomerophyric clusters, including two or three phenocryst phases occur are common in evolved basalts and basaltic andesites. Most HLP 23

basalts have a diktytaxitic texture, although other groundmass textures including

intergranular, subophitic, and ophitic are observed.

Rhyolites were erupted in >60 domes or dome complexes, three major ash

flow tuffs (Prater Creek, Devine Canyon, and Rattlesnake), and several minor tuffs

(Fig. 2.3A). Silicic rocks are mainly high-silica rhyolites (>75 wt% Si02) andare

metaluminous to mildly peralkaline. Rhyolite lavas and tuffsare aphanitic to

moderately porphyritic, with varying combinations of plagioclase, quartz, sanidine,

biotite, hornblende, and clinopyroxene phenocrysts (MacLean,1994; Streck and

Grunder, 1995; Johnson and Grunder, 2000). Intermediate composition volcanic

rocks are uncommon among rocks younger than 11 Ma, andare mainly simple

mixtures if basalt and rhyolite (Linneman and Meyers, 1990; MacLean, 1994;

Streck and Grunder, 1999; and Johnson and Grunder, 2000).

Structure

The transition from the Basin and Range province northward, to the High

Lava Plains, is manifested by northward decrease in reliefon Basin and Range

fault-bounded range fronts and a wide zone of northwest-striking faults of modest normal offset (<100 m) within and south of the High Lava Plains. The Brothers fault zone (Lawrence, 1976) is a concentration of such northwest-striking faults

that cuts obliquely the HLP (Fig. 2.2).

Johnson (1995) documented that both Basin and Range and Brothers fault zone faults were active in the eastern HLP by around 10 Ma. Hart and others 24

\ ) NC \ \( C 4

HB I /% \ \\ --t : ri \

WR

'-S 0'

Hgtr Lava Ptarno 50 Basrrr and Range

t Faults >300 m Topographic Retief

Faults >30Cm Topograporc Relmi

Figure 2.2 Map of faults of the High Lava Plains and northwestern Basin and Range after Walker and MacLeod (1991).

(1984) suggested that faulting in the Basing and Range south of the central HLP

(Poker Jim Rim and Abert Rim) occurred between 6 and 7 Ma. Holocene faulting

has occurred on Basin and Range faults south of the HLP andon NW trending faults in the southwestern HLP (Pezzopane and Weldon, 1993).

Previous Geochronology

The west-migrating pattern of silicic volcanism was first described by

Walker (1974). K-Ar ages of rhyolites determined in association with regional reconnaissance mapping were reported by Walker (1974) and McKee and others

(1976). MacLeod and others (1975) presented a series of isochrons (revised here in

Fig. 2.3A) depicting the westward age progression of rhyolites. Additional K-Ar 25

ages for rhyolites in the western Harney Basin were reported by Parker and

Armstrong (1972). In a statewide compilation of K-Ar age determinations,

Fiebelkorn and others (1983) reported other scattered published and unpublished ages and corrected previously reported ages for the currently accepted 40K decay constant.

Many basalts were also dated by the K-Ar method in the course of reconnaissance mapping of southeastern Oregon. Most of those ages were unpublished prior to the compilation of Fiebelkorn and others (1983). Parker and

Armstrong (1972) reported several K-Ar age determinations on Harney Basin basalts. As part of a broad study of late Cenozoic basalts of the northwestern Basin and Range, Hart and others (1984) reported several K-Ar ages for basalts within the study area. Diggles and others (1990) reported K-Ar ages for two basalts from

Diablo Rim. Pickthorn and Sherrod (1990) reported K-Ar ages of basalts in the southwestern portion of the area shown in Figures 2.3. The sole previously reported

40Ar/39Arage is an unpublished age cited by Johnson (1998) for a basalt near

Frederick Butte.

METHODS

Samples were analyzed by the 40Ar/39Ar technique in two labs. A suite of twenty-three samples consisting primarily of rhyolites was analyzed at the Berkeley

Geochronology Center, and thirty-five samples, primarily basalts, were analyzed in the College of Oceanic and Atmospheric Sciences at Oregon State University. 26

Sample preparation and analytical procedures differed between the two labs and are therefore described separately below.

Berkeley Geochronology Center

Samples analyzed at the Berkeley Geochronology Center included 18 rhyolite and dacite lavas, four rhyolitic tuffs, and one basalt. Lavas and tuffs were prepared as sanidine, biotite, and plagioclase mineral separates or crushed obsidian except for one tuff which was prepared as a separate of devitnfied matrix material.

The basalt was prepared as crushed whole rock. Samples numbered HP-91-X were irradiated in the central thimble facility of the Omega West reactor of the Los

Alamos National Laboratory without the use of Cd shielding. All other samples were irradiated in the Cd-shielded CLICIT facility of the Oregon State University

TRIGA reactor. Samples were regularly interspersed with monitor standards in wells drilled in a concentric circular pattern on Al disks. Sanidine from the Fish

Canyon Tuff, with reference age 27.84 Ma (Cebula and others, 1986; Samson and

Alexander, 1987) was used as the neutron fluence monitor.

Seventeen samples were analyzed by the laser total fusion method using a focused Ar-ion or Nd-YAG laser (Table 2.1). In these experiments, 6 to 15 single grains of sanidine, plagioclase, or obsidian glass were analyzed per sample. Four samples were analyzed by incremental heating using a defocused Ar-ion laser, all of which were run in duplicate (Table 2.2). Samples for laser fusion or heating were loaded in to a copper sample holder and baked at 200 °C overnight. Two samples 27

were heated incrementally employing a double-vacuum resistance furnace (Table

2.2). Isotopic measurements were made in a Mass Analyzer Products MAP-215150 noble-gas mass spectrometer.

Oregon State University

Samples analyzed at OSU (Table 2.3) were prepared as either whole-rock mini-cores (-100 mg), groundmass separates, or mineral separates (plagioclase).

Samples and monitors (Fish Canyon Tuff biotite, FCT-3, 28.04 Ma)were stacked in quartz tubes and irradiated at the TRIGA reactor facility at OSU. Neutron flux was determined by analysis of monitors. Samples were degassed at 400 °C for 20 minutes, then analyzed in a series of stepwise heating experiments with increments ranging from 50 to 200 °C to optimize instrumental operating parameters. Samples were heated in a low-blank tantalum resistance furnace with a programmable electronic control unit. Gases produced during heating were cleaned by sequential exposure to Zr-Al getters. Analyses were made with a Mass Analyzer Products

MAP-215/50 mass spectrometer operating in peak-hopping mode (Duncan and

Hogan, 1994; Duncan and others, 1997).

RESULTS

Of the 201 laser total-fusion analyses summarized in table 2.1, six fell more than two standard deviations beyond their weighted mean sample ages and were rejected from further analysis. Age probability spectra for the remaining laser total- fusion ages are near Gaussian for18 samples, while one sample (HP-91-2) yielded

a bimodal distribution (Figs. 2.4 and 2.5). Good correspondencein mean age was

found between coexisting sanidine andnon-hydrated obsidian (HP-91-10), and

between sanidine and plagioclase (HP-91-14).

In all but one of the incremental heatingexperiments conducted at the Berkeley

Geochronology Center (Table 2.2), incrementalheating spectra yielded apparent

age plateaus using the definition of Fleck and others (1977) (threeor more

contiguous steps concordant at 2, and constitutinggreater than 50% of the 39Ar

released in the incremental heating experiment).Data were also plotted on 36Ar

/40Ar-39Ar /40Ar isochrondiagrams ("inverse isochron"). Plateauages are

concordant with the isochronages calculated from plateau steps, with isochrons

meeting the statistical population criteria ofMSWD (mean sum of weighted

deviates) less than critical values definedby Mahon (1996). If the trapped argon

component indicated by the isochron plotwas within 2of the atmospheric composition (40Ar I36Ar= 295.5), the plateau age was accepted as the preferred age. The trapped component implied by the isochron plot forone analysis of HP-

91-4 is beyond 2c of the atmospheric ratio,so the isochron age is the preferred age for this sample. For samples whichwere run in duplicate, by either incremental heating or laser total-fusion, the weightedmean of both ages is reported and taken to be the best estimate of the age of the sample.

Of the 36 incremental heating experiments conductedat Oregon State

University (Table 2.3), 26 yielded plateaus withages concordant (at 2) with Table 2.1. Summary of Single-Grain Laser Total-Fusion 40Ar/39Ar Results

Sample Dome or Tuft Rock Material Number Average Weighted Mean ± Type Datedt of Analyses% Radiogenic Age (Ma) (in) Accept/Total 40Ar DC-215a Devine Canyon Tuft AFT S 9/10 98.7 988 fLQZ DO-93-13 Double-ORanch A P 13/14 81.0 &2 QQ HP-91-2 Bums Butte R S 8/9 66.8 L Q_Q4 HP-91-7 Little Juniper Mtn. D S 8/8 93.5 QQA HP-91-9 Buckaroo Lake Tuft AFT 5 10/10 87.4 LII Q_Q4 HP-91-10 Horse Mountain D 0 9/9 96.3 7.049 0.018 S 10/10 89.1 7.050 0.030 Weighted Mean L.QQ DQ2J HP-91-12 Rattlesnake Tuft AFT S 15/15 95.7 LQ.4.Z QQ1 HP-91-13 Jumiper Ridge, west R S 15/15 89.8 ZQZ 0Q16 Hp-gl-14 HorseheadMtn. 0 P 9/9 85.9 15.47 0.10 5 6/6 98.0 15.54 0.03 Weighted Mean i. 2Q3 HP-93-2 Sheep Mtn. R S 12/12 97.1 L.1.3J. QSL14 HP-g3-4 Egli Ridge, northwest R 0 9/10 97.8 LQQ Q.Q1r HP-93-13C Wagontire Mountain R 0 7/8 80.6 ZJ2 QQ1fl HP-93-16 Horse Mtn., north R S 14/15 92.0 LZ3 Q18 HP-g3-25 Rams Butte A S 12/12 93.7 L.1Q QiA JJ92-5 lndianCreekButte FO S 10/10 98.5 1QJ. QQ JA-91-25 Juniper Ridge, west R 0 10/10 86.7 Z4 QQiI JR-92-56 Juniper Ridge, east R 0 10/10 98.1 L84 QQi NOTES: underlined, preferred age. * AFT, ash-flow tuft; A, rhyolite; AD, rhyodacite. tS, sanidine; P, plagioclase; 0, obsidian. § age of HP-91-2 is uncertain due to bimodal nature ol probability-age spectrum.

Table 2.2. Summary of Incremental-Heating 40Ar/39Ar Results from Berkeley Geochronology Center

Integrated Sample Dome or Tuft Rock MateriatHeating Plateau lsochron Type DatedtDevice Age (Ma) ± (in) %wArAge (Ma)± (in) **Ar/Ar ± (In)Age (Ma) ± (in) Intercept 6.21 0.06 HP-91-4 Palomino Rote A Bt L 6.29 0.03 71 L3J QQ3 284 4 - 6.25 0.08 Bt L - 2.61 Oil HP-91-5 Iron Mountain R at L 2.83 0.04 58 2.77 0.12 310 25 BI L 2.78 0.11 92 2.96 0.11 283 6 2.60 0.30 Weighted Mean 282 0.24 6.67 0.07 HP-91-ii Elk Butte A at L 6.88 0.03 84 6.86 0.03 298 3 0.10 at L 6.88 0.04 82 6.86 0.04 297 2 6.50 Weighted Mean L88 0.02 10.34 0.07 JJ92-1 Duck Creek Butte A Bt L 10.41 0.04 98 10.43 0.04 290 6 10.42 0.10 at L 1043 0.03 100 10.45 0,06 289 12 Weighted Mean 10.4.2 0.02 1.24 0.16 JJ92-20 Lava near Duck Creek auth a lAR F 1.37 0.04 92 1.41 0.05 294 2 0.20 fAR F 1.29 0.06 100 1.37 0.06 292 2 1.20 Weighted Mean t35 0.03 350 160 8.41 0.09 PC-i Prater Creek Tuft AFT matrix F L41. Qfl9 70 8.36 0.16 NOTES: m,dadead, preferred age.AFT, ash-flow luff; R, rhyolilo; B, basalt. tet, biofile; WR, whole rock. § L, laser; F, furnace. 30

Table 2.3. Summary of Incremental-Heating 40Ar/39Ar Results from Oregon State University

Sample Rock Material Plateau lsochron Intergated f Type Age (Ma) *(in) %39Ar Age (Ma) *(in) 40Ar/36Ar ±(in) Age (Ma) ±(in) Datedt j Intercept 1WHLP99 B VR LQ QJj 100 7.05 0.26 301.0 20.7 6.95 0.22 2WHLP97 B Y 7.90 0.13 83 LZ QJ 307.4 4.4 8.04 0.14 8WHLP97 B WR 33 Qfi 60 3.93 0.06 305.8 5.3 4.06 0.06 13WHLP98 B QJJ. 96 5.46 0.14 316.2 16.6 6.07 0.13 15WHLP98 B Q_Q9 100 5.28 0.13 293.9 10.1 5.17 0.17 24WHLP98 B R Qfl 74 5.76 0.31 305.0 22.2 6.73 0.13 25wHLP98 B 3f Q4Q QQ 100 0.467 0.177 302.7 6.7 0.806 0.072 ------1.84 0.12

3OWHLP98 B fAR ------1.59 0.13 48WHLP98 B fAR 7.95 0.08 66 L1I Q_Q 317.3 4.6 8.06 0.33 74WHLP98 B fAR Ll Q.J 92 7.76 0.12 296.0 6.5 7.61 0.13 76WHLP98 B P1 ------234 25 fAR LQI QQZ 68 0.68 0.25 311.6 20.0 1.48 0.06 8IWHLP98 B fAR 1.74 0.16 98 jQ QIZ 301.6 1.8 1.82 0.14 1O3WHLP98 B fAR 419 QJJ 100 4.63 0.23 396.6 117.4 4.89 0.28 123WHLP98 B 2jQ QJ 78 2.08 0.38 311.7 30.0 2.70 0.15 128WHLP98 B G1 2.92 Q_Q 99 2.82 0.09 307.7 7.9 2.77 0.11 13OWHLP98 B fAR j9Z Q2J. 74 1.82 0.39 303.5 13.7 1.45 0.33 138CHLP98 B G1 ------14.25 2.97

145CHLP98 B fAR 22.QV Q_Q4 56 - - - 2.36 0.05 148CHLP98 B V - - L4 Qfl 322.0 1.8 10.12 0.13 HBA-13.5 B fAR LQ QJJ, 62 7.87 0.24 288.6 5.7 6.37 0.26 HBA-3 B V 44 QJ.Q 52 5.02 0.27 320.6 15.1 5.59 0.14 HLP-98-6a AFT P 12.03 0.51 100 304.1 2.2 13.83 0.63 HLP-98-12 B fAR 59Q Q_Q9 94 5.16 0.63 317.5 18.8 5.60 0.19 HLP-98-24 B fAR Z.J, Q22 100 6.92 0.29 315.1 11.5 6.54 0.51 HLP-98-32 D P QJ, 100 14.79 0.54 310.4 13.5 14.85 0.69 HLP-98-33 B fAR LQ Q_Q 68 7.54 0.11 313.8 10.9 8.03 0.07 HLP-98-35 B fAR ia Qj3 73 16.49 0.24 301.5 6.3 16.62 0.23 HLP-98-40 B fAR jj QQ 91 1.21 0.06 304.0 11.0 1.02 0.13 HLP-98-42 B fAR j_4 Q_Q 91 1.39 0.37 298.1 10.9 1.34 0.17 HLP-98-54 B Ggf J..Q..42 Q_Q 89 10.37 0.09 300.1 4.0 10.64 0.11 HLP-98-59 B fAR Q,jj QL1 81 0.162 0.261 291.5 39.3 0.542 0.164 HLP-98-66 B fAR Z4 Qflj 93 2.50 0.09 321.8 27.8 2.72 0.09 HP-33 B fAR j, Q4 100 7.64 0.61 303.8 6.2 8.23 0.46 JR-91-21 B 2..3Z Q_Q4 89 2.42 0.07 269.2 33.1 2.36 0.07 NOTES: underlined, preferred age.B. basalt; AFT, ash-flow luff; D, dacite. tWR, whole rock; GM, groundmaaa; P. plagioclase. § isochroi, MSWD exceeds crilical value. I Plateau based on4aleps not including most radiogenic steps, isochron based on all steps. two step plateau. 31

isochron ages, with isochrons indicating a trapped argon component within 2c of

atmospheric composition (Fig. 2.6a). Four samples yielded plateaus, which failed

to overlap (at 2) with their isochron ages. The isochrons for these samples

indicates excess argon, and the isochron age is preferred (Fig. 2.6b). One sample

(148CHLP98; Fig. 2.6c) did not yield a plateau but all data lie on an isochron

indicating excess argon; it should be recognized that if the trapped component ina

sample is non-atmospheric, it can't be expected to yield a plateau with ages

generated assuming atmospheric composition for the trapped component. One

sample (145CHLP98) did not yield a three segment plateau, but two precisely

determined sequential releases that constitute 56% of the 39Ar released in this

experiment. We accept the two segment plateau age as the preferred age of this

sample. The remaining three experiments did not produce reliable crystallization

ages. The integrated ages are reported, but we do not consider these as meaningful

age estimates for these samples.

The dating results are consistent with stratigraphic relationships where they

are known, excepting involves three basalts from Egli Rim. Samples from two of

the lowest lava flows in the section (13WH1LP98 and 15WHLP98) yielded ages of

5.58 ± 0.11 and 5.26 ± 0.09 Ma, and a sample from the rim flow (24WHLP98)

yielded an age of 5.89 ± 0.12 Ma. The youngest and oldest of these ages are just

beyond 2of one another. Hart and others (1984) analyzed rim and base samples at

Egli Rim by the K-Ar method, and also reported a younger age from the base of the

section (5.80 Ma rim, 5.21 Ma base). The lower flows are more likely to have been 32

Figure 2.3. (following page) Maps of the High Lava Plainsshowing the distribution of (A) rhyolites and (B) basalts. Bothmaps show the locations of 40Ar /39Ar ages presented in this paper, as wellas previous age determinations, where not superceded by new ages, from Parker and Armstrong (1972), Walker(1974), McKee and others (1976), Fiebelkorn and others (1983), Hartand others (1984), Diggles and others (1990),Pickthorn and Sherrod (1990), and Johnson (1998). Ages reported prior to 1983are shown as corrected by Fiebelkorn (1983) for a change in the 40K decay constant. The 15.9 Maage is weighted mean of two ages reported by Fiebelkorn and others (1983) fora rhyolite dome near Venator. Isochrons on the rhyolite age mapare in 1 Ma increments, and are in part constrained by points off the map to the south. Abbreviationsare: NC=Newberry Caldera, QM=Quartz Mountain, GB=Glass Butte, JR=JuniperRidge, HIvI=Horeshead Mountain, IM=Iron Mountain, PaB=PalominoButte, DB=Duck Butte, DRG=Dry River Gorge, WB=West Butte, PH=PotHoles lava, DG=Devil's Garden lava, ER=Egli Rim, EL=East lava, FC=Four Craterslava, BR=Burma Rim, AR=Abert Rim, PiB=Piute Butte, PJ=Poker Jim Ridge, WP=Wright'sPoint, DC=Diamond Craters. 33

.Rhyolites 121 120 119 118

I .44

NC Prater Creek 0.6\ QM Tuff8.41 I' 234IO. G 15. 24%. . 6.85Pa4)7 63Devine Canyon 6.29 Tuft 9.68 44: 6 Rattlesnake Tuft 7.05 .5 f1 4.5g.5.0 6.88 . u 2.82, 5.2 7.j3 15.53 IM 8.23 10.63Ao.3èI ?723 g1HM 7.05 ' 1.42 8 C 15.34 4.8 9 10

Est. vents for tuffs Fthyolites (<12 Ma) hyolites (14-16 Ma) 76 4 50km Basalts (<12 Ma) p7.9 --

B. Basalts

121 120 119 11 DR&4.7. I NC

7.6 00 W)r WP

. 7.1

.16.68 - I Late Quaternary Basalt (<50 ka) Li Newberry Volcano Basalt (0 & Late 0) Li Quaternary Basalt Pliocene Basalt Miocene Post-Steena Basalt 9 Li Rhyolites (< 15 Ma) o t8 AL 50km

Figure 2.3 34

6-

>' 8. -9

(0 7

0a- a- -4 >0) 10 4- CO .1 3... 0) 11

670 6.80 6.90 7.00 7.10 7.20 7.30 7.4

2J 15L16

6 7 8 9 10 11 12 13 14 15 16 Age (Ma)

Figure 2.4. Age-probability spectra for all samples dated by the laser total-fusion method. The inset figure is an enlargement of the interval form 6.7 to 7.4 Ma. The age probabilities are calculated assuming a unit gaussian error for each analysis, followed by summation across all samples of probabilities within narrow age intervals. Numbers identifying spectra refer to the following samples: 1. HP-91-13, 2. JR-91-25, 3. HP-91-9, 4. JR-92-56, 5. HP-91-1O (obsidian), 6. HP-91-12, 7. HP- 93-4, 8. HP-93-25, 9. HP-93-2, 10. HP-93-13C, 11. HP-91-1O (sanidine), 12. HP- 93-16, 13. HP-91-2, 14. DO-93-13, 15. DC-215a, 16. JJ92-5, 17. HP-91-14 (plagioclase), 18. HP-91-14 (sanidine), 19. HP-91-7. 35

o). Sanidine Obsidian I .1 C')' .1 0 I -ox b.I è.I 100

. 0.040

0C 0.020 [I I =2=--. 10

-SO) > I ' 0

-c 0 0 >U)

U) a: P-.-17.05±0.04 117.049±0.018 6.8 7.0 7:2 6.8 7.0 7.2 7.4

Age (Ma)

Figure2.5.Age probability diagrams for auxiliary plots of 40Ar /39Ar analytical data (moles 39Ar, percent radiogenic 40Ar [40Ar *], Ca/K ratio, and a display of individual analyses) for laser total-fusion dating of coexisting obsidian glass and sanidine from sampleHP-91-1Ocollected from Horse Mountain. The mode of each spectra is shown near the peak of the curves. Error bars near the bottom represent the standard error of the weighted mean, both with (outer ticks) and without (inner ticks) error in J, the neutron fluence parameter. 36

A 10 HLP-98-66 0.0040 8 Whole Rock

(5 0.0030 2.54 ± 0.07 Ma E0.0020 a

0.0010

0.0000 7 0 102030405060 708090100 0.0 0.2 0.40.60.8 1.0 1.2 1.4 1.6 Cumulative 39Ar Released (%) 39Ar/40Ar

B. 10j 8IWHLP98 Whole Rock 0.004 I

(5 - 0.003 4

(5 4 0.002

0.0011

0.0001 0102030405060708090100 000 050 1.00 1.50 2.00 Cumulative 39Ar Released (%) 39Ar/40Ar 40 c. 148CHLP981 0.0040

30 7.54 ± 0.07 Ma (5 0.0030 4O/36 = 322.0 ± 1.8 25 MSWD = 0.53

20 . 0.0020

15

10

4 0.00 0.10 0.20 0.30 0,40 Cumulative 39Ar Released (%) 39Ar/40Ar

Figure 2.6. Representative plateau and inverse isochron plots for incremental heating analyses performed at Oregon State University. Segmentson plateau plots are shown with 2c uncertainty. On isochron plots, shaded squares are data used to determine isochrons;

heated or altered, resulting in some argon loss, so the rim flow age is considered the

best estimate of the age of the sequence.

Where the new ages for rhyolitic units are 40Ar/39Ar analyses of units

previously dated by the K-Ar technique, the new data are typically ten times more

precise and a little older. The ages for the Devine Canyon (9.68 ± 0.02 Ma), Prater

Creek (8.41 ± 0.09 Ma), and Rattlesnake Tuffs (7.047 ± 0.015 Ma) have been

precisely determined and lie within error of the oldest ages reported for these units;

previous K-Ar ages ranged over more than 2 m.y. Morphologically youthful basalts

yielded Quatemary ages. Three dacitic centers yielded 15.3-15.5 Ma ages and

expand the distribution of known silicic volcanism of Middle Miocene age (Fig.

2.1). One basalt from the lower portion of a section near French Glen yielded an

age of 16.68 ± 0.13 Ma. This age coincides, at 1, with ages reported for the entire

sequence of Steens Basalt exposed on Steens Mountain (16.58 ± 0.05 to 16.59 ±

0.02 Ma; Swisher and others, 1990), indicating that this is a Steens Basalt.

DISCUSSION

Propagation of Rhyolitic Volcanism

New rhyolite ages confirm the contention of Walker (1974) and MacLeod

and others (1975) that silicic volcanism is progressively younger to the west along the High Lava Plains. The new ages require revisions to the isochrons of MacLeod

and others (1975), but their general form remains the same (Fig. 2.3A). Two new rhyolite dome ages are not easily reconciled with a simple set of isochrons: Iron

Mountain (2.82 ± 0.04 Ma), which had been previously recognized as much younger than the trend, and Palomino Butte (6.29 ± 0.03 Ma) which is only slightly younger than predicted by the trend. The estimated positions of the eruptive centers for the Prater Creek and Devine Canyon Tuffs also do not correspond with the pattern of isochrons. The locations of these eruptive centers are not well constrained, and the isochron pattern suggests that their sources may be further east

The pattern of isochrons in Figure 2.3A suggests migration of silicic volcanism along a front. The general trend of the isochrons is northeast, so if propagation were as a wave perpendicular to the front, propagation would have been to the northwest. This was apparently not the case as this would have led to propagation from Duck Creek Butte in to the Blue Mountains province to the north.

Rather, from Duck Creek Butte, the belt of maximum rhyolitic volcanism trends

-N75°W, along the axis of Pliocene and younger basaltic volcanism. These observations suggest that the front of migrating silicic volcanism trended northeast initially, then migrated -N75°W. Relatively young ages in the north-central and western HLP require that these isochrons reorient to trend east-northeast, suggesting changes in the geometry of the front (Fig. 2.3A). The isochrons also become more closely spaced in this area suggesting a decline in the rate of propagation to -14 kmlm.y.. Alternatively, these young ages could be interpreted to reflect prolonged silicic volcanism after the passage of the front. '1,]

1 Rhyolite - New Age I . RhyolitePrevious Age Basalt New Age 10 oBasaltPrevious Age I

jiti

I I I 4 TL U

2 U TVC U11 SNV [I] 300 200 100 0 Distance (km) Along The High Lava Plains Measured Westward from Duck Butte

Figure 2.7. Plot of previous and new rhyolite and basalt ages versus distance along the HLP trend. Data are projected N15°E or S15°W to the axis of the N75°W- trending belt of Quaternary HLP basalts. Error bars indicate 1error. Sources of previous ages are those cited in Figure 2.3 plus ages for silicic tuffs erupted from the Tumalo volcanic center (TVC) from Sarna-Wojicki and others (1989). Also shown are Quaternary silicic lavas erupted at Newberry Volcano (NV) and South Sister (SS). Dashed line represents the eastern border of the Cascade Range. The yellow field indicates the silicic age progression as interpreted here: 35 kmlm.y. from 10.5-5 to 5 Ma and 14 km/m.y. from 5 Ma to Recent, with a 2 m.y. duration of rhyolitic volcanism at any given point along the trend. These conflicting interpretations were also explored by considering age of silicic volcanism versus distance along the trend (Fig. 2.7). A field can be drawn around most of the data from 11 to 5 Ma that includes two million years of silicic volcanism at any point along the trend. The slope of the axis of this field indicates a propagation rate 35 km/m.y. Projecting this field westward the trend intersects the

Cascade Range consistent with Quaternary silicic tuffs erupted from the Tumalo volcanic center (Sarna-Wojcicki and others, 1989) and Recent silicic domes near

South Sister (Fig. 2.7). That the current focus of the trend is near South Sister has been previously suggested by Hill and Taylor (1989).

The field of projected volcanism extending from the central HLP to the

South Sister area misses not only Newberry Volcano, but all of the silicic domes of the western HLP, so our preference is to consider the present endpoint near

Newberry Caldera. In this view, rhyolitic volcanism at South Sister may be unrelated to the HLP trend (young silicic volcanic rocks are found in the Cascades north and south of this point; Sherrod and Smith, 1989). We do not necessarily interpret Newberry Volcano to simply be the Recent focus of the HLP trend, but rather interpret it as reflecting the interaction of processes responsible for HLP and

Cascade magmatism. Helium isotope data for Newberry flank lavas suggest an affinity for the Cascade range (Chapter 3).

An episode of particularly voluminous silicic volcanism appears to have occurred between 7.0 and 7.2 Ma. In this time the Rattlesnake Tuff, one of the 41

largest tuffs in the High Lava Plains (-280 km3; Streck and Grunder, 1995), was

erupted, as were five distinct rhyolite domes.

Middle Miocene Silicic Magmatism

We report new ages for three dacite domes, Horsehead Mountain (15.53 ±

0.03 Ma), Little Juniper Mountain (15.55 ± 0.04 Ma), and Jackass Butte (15.34 ±

0.19). Previous workers have reported ages of 15-16 Ma for four other silicic

domes in the HLP and adjacent northern Basin and Range (Fig. 2.3A; 16 .0 ± 0.4

Ma Drum Hill Dome is just south of map area). The Middle Miocene silcic domes

are distinct from rhyolites of the HLP age progression in that they are predominantly dacite and rhyodacite-rhyolite, and rarely high-silica rhyolite

(MacLean, 1994). These ages coincide with ages of widespread ash-flow (tuft)

volcanism in southeastern Oregon and north-central Nevada, including McDermitt

Caldera (as summarized by Pierce and Morgan, 1992).

This episode of silicic volcanism follows the initial eruptions of the

Columbia River basalts (CRB) and Steens Basalts, and coincides with the most

voluminous phase of the CRB (Grande Ronde Basalt). Many workers interpreted the Steens and CRB eruptions as the result of the head of the Yellowstone plume impinging upon the base of the lithosphere (e.g. Thompson and Gibson, 1991;

Geist and Richards, 1993; Camp, 1994; Hooper, 1997). Pierce and Morgan (1992) interpret widespread silicic volcanism at this time to also reflect the plume head phase of the Yellowstone plume. If this is the case, then the occurrence of middle 42

Miocene silicic volcanic rocks across more than half of the length of the HLP indicates the minimum extent of this plume head.

Timing of Basaltic Volcanism

Basalt ages have no clear systematic spatial variation (Fig. 2.7), although several generalizations can be made. The oldest basalts (post-Steens) dated in the east are older than those in the west. This may simply reflect the lack of deep exposure in the west. In the northern Basin and Range there is a coarse westward progression in the age of cessation of basaltic volcanism, with no Pliocene basalts east of -121 °W (in the map area). Quaternary basalts are limited to the axis of the

HLP, and are sparse in the central HLP (Fig. 2.3).

Figure 2.8 depicts new and previously reported ages for High Lava Plains basalts in two ways. The curve in Figure 2.8A represents the cumulative relative probability of basalt ages based on reported uncertainties, a strict statistical depiction of the data. The histogram (Fig. 2.8B) shows the frequency of ages within

250 k.y. of each 100 k.y. increment. The value of the latter plot is that it reflects the perspective that sampling is incomplete, though the bin range is somewhat arbitrary. These plots suggest that HLP basaltic volcanism has been continuous, with possible episodes of increased activity centered on 7.6, 5.9,and 2-3 Ma. In the eastern HLP there seems to be a period of inactivity between 7 and 3 Ma, while in the western HLP basaltic volcanism is more continuous (Fig. 2.7). >

-o 0 I.-

C) 4-

C)

>ci) 4-a C', E

0 1 2 3 4 5 6 7 8 9 10 11 Age (Ma)

> '-7C', 0

C',

LC) C +1

0) 4-0 > C20 C) Wi U-

0 1 2 3 4 5 6 7 8 9 10 11 Age (Ma)

Figure 2.8. Statistical plots of previous and new ages for HLP basalts. (A) curve shows the cumulative (all dates under one curve) relative probabilities of ages assuming a gaussian distribution about the reported ages based on1uncertainties. (B) histogram shows the frequency of ages (regardless of error) within 250,000 years of each 100,000 year increment. Both curves suggest rather continuous basaltic volcanism with episodic flare-ups. 44

The 7.6 Ma episode is the most robust of the suggested episodes. Eight of

the 40Ar /39Ar ages reported in this paper overlap within 2with an average of

7.60 Ma (excluding the relatively imprecise 8.21 Ma age of HP-33). These samples

span nearly 200 km of the HLP, suggesting a major regional event, perhaps related to an early phase of activity on the Brothers fault zone. This event preceded one of the largest episode of silicic volcanism (-7.1 Ma; focused in the central HILP) by half a million years. Also, the timing of this 7.6 Ma event corresponds with the initiation of the ongoing High Cascades phase of Cascades volcanism and tectonism (estimated initiation age of 7.4 Ma; Priest, 1990). We envision these events as related by the following scenario: at around 7.6 Ma there was a change in either the relative plate motion at the continental margin, or the geometry of subduction; this change led to initiation of a new phase of Cascade volcanism and tectonism, and deformation along the Brothers fault zone to the east; activation of the Brothers fault zone allowed more mafic magma to intrude and traverse the crust leading to widespread basaltic volcanism; accumulation of basaltic magmas stalled in the crust led to anomalously high rates of production of crustal melts in the following half million years.

The 5.9 Ma episode is suggested by ages for basalts mostly in the northern

Basin and Range, including samples at Egli and Burma Rims at the extreme northern margin of the Basin and Range. The 2-3 Ma episode is suggested by widely distributed ages along the axis of the High Lava Plains. Included in this 2-3

Ma episode are several compositionally anomalous volcanic units. The basalt flows 45

underlying the Grassy Butte cinder cone in the western HLPare 2.92 ± 0.06 Ma.

These basalts are coarsely olivine-phyric and are characterized bya unique

combination of high MgO (8.31 wt%) and high incompatible element abundances

(K20=1.52 wt%, Ba=ll85ppm). A similar basalt (dated at 3.98 ± 0.06 Ma) is

found overlying a significant angular unconformity exposed in the Dry River Gorge

to the west. Also in this period was the eruption of the basaltic trachyandesite of

Paiute Butte in the central HLP (2.37 ± 0.04 Ma). This unit is characterized by high abundances of K20 (2.10 wt%) and Ba (1552 ppm), and is interpreted to reflect extreme crystalfractionation and recharge (MacLean, 1994). It is notable that the silicic volcano falling most off of the HLP trend, Iron Mountain, also occurs in this time interval (2.82 ± 0.04 Ma).

An age was determined for the Green Mountain basalt in which the feature

Crack-in-the-Ground is developed. Pezzopane and Weldon (1993) interpreted this feature as resulting from faulting after emplacement of the lava. From the age of this unit (740 ± 59 ka) and the displacement reported by Pezzopane and Weldon

(1993), we calculate a minimum deformation rate on this structure of 0.013 mm/yr.

Comparison of the HLP and YSRP Trends

As the HLP and YSRP trends have been proposed to be linked, we compare the trends and consider the implications for the origins of both. The propagation of the YSRP trend is generally represented by a series of calderas (Fig. 2.1), from

McDermitt on the Oregon-Nevada border (-46.1 Ma) to the Yellowstone Plateau (0.6 Ma). The length of this track is 690 km, withan average rate of propagation of

43 kmlm.y. to -N65°E. Pierce and Morgan (1992) proposed two distinct legs (16-

10 Ma, 70 km/Ma to N75°E; and 10-0 Ma, 29 km/m.y. to N54°E), and Smith and

Braile (1994) suggested a slightly different representation (16-8 Ma, 61 km/m.y. to

N73°E; and 8-0 Ma, 33 km/m.y. to N54°E).

If the YSRP trend is considered the result of a stationary mantle plume, the above described propagation rates are in conflict with the motion of the North

American plate estimated by global plate motion models (Gripp and Gordon, 1990;

Duncan and Richards, 1991; see Fig. 2.1), especially prior to 10 Ma. Smith and

Braile (1994) suggest that this conflict can be reconciled by considering extension along the length of the trend. However, Rodgers and others (1994) estimated extension immediately south of the Snake River Plain to be -20%, nowhere close to the 100-300% required to reconcile the length of trend, as generally presented, to the plate motion models. Another potential explanation for this inconsistency is the motion of hotspots. However, when the model of Steinberger and O'Connell

(2000), which successfully predicts the relative motion of Pacific hotspots, is applied, the prediction is for a shorter trend with a more easterly azimuth.

We follow Thompson and Gibson (1991) in suggesting that at 17 Ma the hotspot may have been right where global plate motion models suggest that it was, in southwestern Idaho, near the southern end of the Snake River Plain physiographic province. In this perspective, Middle Miocene basaltic volcanism

(Columbia River and Steens) occurred where plume head material reached thin 47

lithosphere (west of the craton margin as represented by the 87Sr/86Sri > 0.706 line in Figure 2.1). Silicic volcanism, which was widespread between 17 and 10 Ma, reflects more complex interactions between the plume head and North American lithosphere. The rate of propagation of YSRP magmatism after 10 Ma (-29 kmlm.y.) is more consistent with that predicted by plate motion models plus extension (maximum of 25 km/m.y.).

Between 10 Ma and 5 Ma, the trends have similar propagation rates, but there is no evidence for a slowing at 5 Ma in the YSRP as is observed for the HLP.

As has been described by Pierce and Morgan (1992) and Smith and Braile (1994) there are other significant differences in the two trends, notably in types of silicic eruptive products (HLP mostly domes; YSRP mostly tuffs), volumes of silicic volcanic rocks (HLP eruptions up to 300 km3; YSRP >2000 km3), and structural setting. However, given the extreme contrast in the character of the lithosphere on which the trends are developed, even if they were caused by the exact same tectonic process, it may have been manifested differently in the two areas.

If the YSRP trend is the result of plate motion over a fixed hotspot, then the absolute motion represented by the HLP trend is the sum of the velocity vectors of the HLP and YSRP trends. Using the simplifying assumption that propagation of the HLP trend was to N75°W at a rate of 35 krnlm.y. between 10 and 5 Ma, and slowed to 14 kmlm.y 5 Ma to Recent, the motion relative to the YSRP reference frame is 58 km/m.y. to S82°W from 10-5 Ma, and 39 km/m.y. to S70°W from 5-0

Ma. We view the divergence of the trends away from the axis of Middle

Miocene basaltic volcanism, and the existence ofa belt of Pliocene and younger

basaltic volcanism continuous across both trendsas strongly suggestive of a link

between the two trends. That they are linked does not require that the HLP and

YSRP trends be generated by the exact same process, but does suggest that the

processes responsible for these trends may be related.

Cause of Migrating Volcanism of the HLP

Based on the results discussed above and the current understanding

of the regional geology we critically revisit the previously proposed models explaining the HLP trend. Christiansen and McKee (1976) and Christiansen (1993) proposed that the HLP and YSRP are the result of propagating rifts or shear zones.

This model does not work for the YSRP because there is neither structural evidence of a shear zone nor a significant change in magnitude of extension across the plain to justify a one. This model is more plausible for the HLP because the volcanic province overlaps with the Brothers fault zone. Comparison of faulting of rocks of similar age in the western and eastern HLP allows a test of the hypothesis that the

Brothers fault zone has propagated across the HLP. Qualitative examination of spacing and apparent displacement of faults cutting 7-8 Ma rocks and 2-3 Ma rocks across the HLP reveals that the spacing and apparent displacement are similar in the east and the west on rocks of similar age. This suggests the Brothers fault zone has not propagated, but rather has been activeacross the entire HLP since at least

-8 Ma.

The evolving back arc model (Carison and Hart, 1987) is not readily

addressed by the data presented here, butwas developed from the perspective that

considerable post-Middle Miocene extension had occurred (basedon

paleomagnetic results in the Coast Range), when the geologic structures suggest

very limited extension (<10%) in southeastern Oregon in this time (Wells and

Heller, 1988).

The model of Humphreys and others (2000) makes no comment on the

origin of Middle Miocene magmatism but suggests that decompression resulting

from spreading and shearing of the residuum of this magmatism caused HLP and

YSRP volcanism. That the HLP propagation rate is, at least prior to 5 Ma, similar to the convergence rate at the Cascadia subduction zone supports this model in a

general way. However, neither the HLP trend or YSRP trend departs from the area that was the source of the bulk of the Middle Miocene magmatism (northeast

Oregon and southeast Washington). Also, helium isotope data (Chapter 3) do not support a direct link between the trends' sources implied by the model.

The model of Draper (1991) attributes the HLP trend to entrainment of plume head material in the subduction induced counter flow cell. This is also consistent with the similarity between propagation rate and the plate convergence rate. However, the model is not consistent with the current understanding of plume head dynamics in which plumes flatten as they approach the lithosphere (Griffiths 50

and Campbell, 1991), and are emplacedacross areas as large as 2,000 km diameter in periods of a few million years (Saunders and others, 1997).

We do find the evidence for a mantle plume origin for the YSRP (e.g.

Pierce and Morgan, 1992; Smith and Braile, 1994) compelling, and favor interpretations that link Middle Miocene large igneous province development to the head of this plume (e.g. Brandon and Goles, 1988; 1995; Hooper, 1997). Several models have been proposed to explain the observation that the bulk of lavas erupted in the Middle Miocene event (the Columbia River basalts)were erupted from vents

>300 km north of Middle Miocene rhyolite volcanic centers of the YSRP trend. We prefer the model of Thompon and Gibson (1992), in which voluminous plume related magmatism occurs only where plume material can rise to shallow depths and undergo decompression melting. Clearly, some large igneous provinces have been emplaced under thick Precambrian lithosphere (e.g. Karoo, Parana, North

Atlantic Igneous Province), but these appear to reflect larger more productive plumes (large igneous province volumes an order of magnitude larger). We prefer the Thompson and Gibson (1991) model because the model of Geist and Richards

(1993) relies upon an unnecessary and poorly understood process (plume-slab interaction), and while the model of Camp (1995) recognizes the significance of basal lithosphenc structure, it places thel7 Ma plume too far west as per the discussion above.

Plume processes could also have had effects under southeastern Oregon.

Even a relatively small flattened plume head emplaced under southwestern Idaho 51

would have extended across much or all of the HLP. Evidence that this was the

case is the presence of 15-16 Ma silicic volcanic centers across the eastern and central HLP, and eruption of the Picture Gorge Basalts in the central Blue

Mountains west of the main axis of Middle Miocene volcanism. Such a plume head

would have the greatest effect where emplaced under thin lithosphere, west and north of the Sr-isotope discontinuities as depicted in Figure 2.1. Because greater

volumes of, and hotter, plume head material would have been emplaced under the eastern HLP than the western HLP, crustal magmatism driven by the conductive

and advective heat and mass transfer would have occurred earlier in the east than the west. This could explain propagation of HLP silicic volcanism.

In this model, the shapes of HLP isochrons would reflect the initial distribution of plume head material and preexisting lithospheric structure. The

abrupt northward termination of the Brothers fault zone occurs immediately north of the belt of Pliocene and younger basaltic volcanism and the northernmost HLP rhyolites. Coinciding with this area is the distortion of the isochrons of rhyolitic

volcanism. We believe that these observations suggest the presence of a preexisting

lithospheric boundary at this position, trending nearly east-west. This boundary would separate relatively thin weak lithosphere to the south (HLP) from thicker

stronger lithosphere to the north (Blue Mountains). 52

Figure 2.9. (following page) Cartoon depicting the scenario envisioned to explain the distribution of Middle Miocene basaltic vents, and trends of migrating silicic volcanism of the HLP and YSRP. (1) the Yellowstone plume head flattens as it approaches the North American lithosphere; (2) magmatism (Columbia River basalt, Steens Basalt, and Northern Nevada Rift; orange lines on map) occurs where the plume head is allowed to rise to shallow depths, especially at the edge of the craton where secondary flow of plume head and perhaps plume material increases activity of the system; (3) as the North American plate moves southwest, the plume becomes established under the continent (no longer connected to the topographic gradient at the craton margin) and leaves a distinct hotspot trace leading to the Yellowstone Plateau; in the west, crustal volcanism migrates westward due to a time lag produced both by conductive heating of the lithosphere and a decrease in mantle advection westward where cooler plume head material was emplaced. 53

Al -: £ Plume hoed diameter = 1100 km £ LA A ZI

A :Jj.._-.- JMigratrng crustal magmatism

\rf \\ due to conductive and advective A heat transfer from plume head I occurs only where plume head 40

I emplaced under thin extending I lithosphere \N 00 km \N \ \\.\\ 120 11O

HLP trend develops due to increased YSRP trend develops0 Ma incubation time for lithopheric magmafism as plate moves over further from center of plume head plume conduit

Melting occurs in plume head 1 7 Ma only where emplaced under thin lithosphere, yet near hot center - -- Plume head has little direct effect where emptaced 4 under thick lithosphere Secondary flow - may explain duration of GlIB eruptions, and lack of early hotspot track

l7Ma

Plume head flattens approschlng the lithosphere

Figure 2.9 54

To summarize the above discussion, we envision the following events leading to the observed age and spatial distribution of middle Miocene and younger rocks of the HLP, YSRP, and Columbia River and Steens Basalts:

1. A modest sized plume head flattened to -1,100 km diameter as it

approached the North American lithosphere at about 17 Ma.

2. The flattened plume head was emplaced at -17 Ma, centered near

soutwestem edge of the Snake River Plain physiographic province as

predicted by global plate motion models. Where emplaced under thick

Precambrian lithosphere (east of Oregon-Idaho border) there was little

immediate effect because the plume head did not decompress sufficiently

to partially melt. Where emplaced under thin lithosphere, yet relatively

near the center, large volumes of basaltic magma (Steens Basalt and CRB)

were generated by decompression melting in the plume and interaction

between the plume and the lithosphere.

3. Between 17 and-14Ma voluminous basaltic magmatism continued, and

silicic volcanism was widespread in the area between the center of the

plume head and craton margin. Basaltic magmatism may reflect

secondary flow of plume material along the slope of the base of the

lithosphere from under thick lithosphere to thin lithosphere.

4.As the North American plate migrated southwest(14-0Ma), the

connection between the plume and craton margin ended and crustal 55

melting above the plume conduit generated the northeast-younging belt of

calderas of the Snake River Plain and Yellowstone Plateau.

5. Where plume head material had been emplaced under thin, modestly

extending, lithosphere west of the craton margin, melting in the plume

head and lithospheric mantle drove crustal melting. This occured first in

the east (more and hotter plume head material) and later in the west,

generating the belt of silicic domes and tuffs of the High Lava Plains and

northwestern Basin and Range province. The distribution of this

magmatism was controlled by regional lithospheric structure, and local

structural development (Brothers fault zone).

CONCLUSIONS

We have reported new 40Ar /39Ar ages (laser total fusion, laser incremental heating, and furnace incremental heating) for 23 rhyolitic units and 32 basaltic units of the High Lava Plains of central and southeastern Oregon. The rhyolite ages confirm the previous interpretation that ages of silicic volcanism are progressively younger to the west. Three regionally significant tuffs have been dated with high precision. A major pulse of rhyolitic volcanism is recognized at 7.0-7.2 Ma. Major episodes of basaltic volcanism are recognized at 7.60 Ma, 5.8 Ma, and 2-3 Ma. The first of these episodes may be regionally significant as it is widespread, corresponds to a major change in deformation and magmatism in the Cascade Range, and precedes the pulse of rhyolitic volcanism by less than half a million years. 56

The HLP trend crudely mirrors the northeast progression of silicic volcanism of the Snake River Plain to the Yellowstone plateau. In light of the co- origination of these trends, their similar bimodal character, and the band of

Pliocene and younger basaltic volcanism continuous across both provinces, it seems unreasonable to consider these trends unrelated. We propose a model in which the YRSP reflects the motion of North America over a mantle plume, the sites of eruption of the Columbia River and Steens Basalts mark the positions where the Yellowstone plume head was emplaced under thin lithosphere yet near the center of the plume, and the HLP trend is a delayed effect of plume head emplacement with increasing incubation times required for lithospheric magmatism farther from the center of the plume head.

ACKNOWLEDGMENTS

Some samples analyzed in this study were collected by Martin Streck, Jenda

Johnson, and Jim MacLean. We are grateful to Lew Hogan and John Huard for their assistance in the geochronology lab at Oregon State University. Jordan also thanks the NSF RIDGE program for funding his participation in the Iceland

Summer School focused on plume-ridge interactions. This work was supported by the National Science Foundation (EAR-9725 166) and by a student research grant from the Geological Society of America. 57

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CHAPTER 3

HELIUM ISOTOPE COMPOSITION OF BASALTS OF THE OREGON HIGH LAVA PLAINS: BEARING ON RELATIONSHIP TO YELLOWSTONE-SNAKE RIVER PLAIN MAGMATISM

Brennan T. Jordan'

David W.Graham2

Anita L.Grunder1

'Department of Geosciences, Oregon State University, Corvallis, OR 97331

2College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331

For submission to Geochimica Cosmochimica Acta ABSTRACT

The High Lava Plains province of central and southeastern Oregon isa

bimodal volcanic field characterized by west-migrating silicic volcanism. This

pattern of migrating volcanism mirrors the pattern of eastward migration of silicic

volcanism across the Snake River Plain to the Yellowstone Plateau, and its

existence is the most frequently cited evidence againsta mantle plume origin for

the Snake River Plain. We have tested the relationship between these two provinces

by studying the helium isotope composition of High Lava Plains basalts. 3He/4He

ratios measured in High Lava Plains basalts are about nine times the atmospheric

ratio (9RA).The helium isotope composition of Newberry Volcano, near the

western end of the High Lava Plains, is 7.6-8.0RA,indicating its affinity with the

Cascade Arc. High Lava Plains 3He/4He ratios of 9RAare lower than values reported for the Snake River Plain and Yellowstone (13-17RA),and near the upper limit observed in mid-ocean ridge basalts (MORB) unaffected by hotspots. The similarity to MORB suggests derivation from a highly depleted mantle source.

Other geochemical evidence suggests, however, an enriched source. This dichotomy might be explained by involvement of two sources. We prefer a model in which the sources are a helium-rich mantle source having high 3He/4He (the

Yellowstone plume), plus an enriched mantle source located either in the asthenosphere or lithosphere. The distribution of these sources may be related to emplacement of a flattened plume-head which had mixed with 65

asthenospheric/lithospheric mantle during ascent. Such a mechanism can also be reconciled with migrating silicic volcanism of the High Lava Plains.

INTRODUCTION

The High Lava Plains physiographic province (HLP) of central and southeastern Oregon is a volcanic upland underlain by basalts and rhyolites of

Miocene and younger age. Rhyolites of the HLP decrease in age, from 10.5 Ma in the east to Recent in the west, where the trend intersects the Cascade Range

(Walker, 1974; MacLeod and others, 1975;Chapter 2). This pattern of migrating silicic volcanism co-originates with, and crudely mirrors, an apparent northeast migration of silicic volcanism across the Snake River Plain to the Yellowstone

Plateau (e.g. Armstrong and others, 1975; Pierce and Morgan, 1992; Smith and

Braile, 1994). The HLP and Yellowstone-Snake River Plain system (YSRP) also appear to be linked because they constitute a relatively continuous band of Pliocene and younger basalts.

The trend of volcanism of the YSRP is consistent with the motion of the

North American plate over a hotspot or mantle plume. The mantle plume model makes no account for west-migrating volcanism of the HLP, therefore the HLP trend is frequently cited as evidence against a mantle plume origin for the YSRP

(e.g. Hamilton, 1989). Other aspects of YSRP volcanism that are not readily explained by the mantle plume model, as developed based on oceanic hotspots, are: the persistence of basaltic volcanism more than ten million years after the passage of the hotspot; and the inconsistency between the generally interpreted hotspot

track length (-700 km) and the length predicted by absolute plate motion models

(200 to 360 km in 17 Ma; based on Engebretson and others, 1985 and Gripp and

Gordon, 1990, respectively) plus extension (-20%; as documented south of the

Snake River Plain by Rodgers and others, 1994).

Models have been developed which can potentially explain these apparent

contradictions. Draper (1991) proposed that the HLP trend reflected westward drag

of plume head material in subduction-induced asthenospheric counterfiow. Lateral

spreading (perpendicular to the direction of propagation) of the buoyant residue of

mantle melting, as described by Humphreys and others (2000) can explain the

persistence of mafic magmatism, as the underlying mantle is decompressed during

spreading. Volcanism away from the center of the plume, potentially explaining the

misfit with predictions based on plate tectonic models, can be explained by melting focused under thin lithosphere as described by Thompson and Gibson (1991).

In addition to the trend of rhyolitic volcanism along the YSRP, the most frequently cited evidence in favor of the mantle plume model is the observation of high 3He/4He ratios, between 13 andl7RA(whereRA= the atmospheric ratio of

1.39 x 106), measured in basalts and hot springs (Craig and others, 1978; Kennedy and others, 1985; Craig, 1997). Elevated 3He/4He ratios of 11.4RAhave also been reported for the Imnaha Basalt, the early phase of the Columbia River Basalt Group

(CRB), supporting a link between the CRB and the YSRP (Dodson and others,

1997). High 3He/4He ratios, >10RA,are commonly found in association with CR) 200 km CR8 ?

45°

NV : 78(vcD7.13j70:

400

4.6-7.1 : : : He-isotope \

anafrses : : : (R/RA) ) : : 4.5-5.5 --350 120° 115° 1100

Figure 3.1. Map showing previous helium isotope determinations in the western United States. Stars indicate new data presented here. Sources of other data include: Cerling and Craig (1994), Craig (1997), Craig and others(1978), Dodson and others (1997; 1998), Kennedy and others (1985), Licciardi and others (1999), Poreda and Craig (1989), and Reid and Graham (1996). Abbreviations: HLP-High Lava Plains, NV-Newberry Volcano, YSRP-Yellowstone-Snake River Plain (dark dashes separate the western Owyhee Plateau, central Snake River Plain, and eastern Yellowstone Plateau), CRB-Columbia River basalts, B&R-Basin and Range, and CR-Cascade Range.

hotspot volcanism (e.g. Farley and Neroda, 1998). This signature is generally taken to reflect input from a relatively undegassed source, commonly interpreted as lower mantle material advected toward the surface by a mantle plume. Alternatively,

Anderson (1998; 2000) proposed that high 3He/4He is a reflection of low 4He, rather than high 3He, and that the source of such characteristics may be the lithosphere or shallowest upper mantle anomalously depleted inU relative to He.

The generally low helium concentration in high-3He/4Hemagmas is usually cited

as evidence of this (Anderson, 1998; 2000), despite the fact that such basaltsare

usually erupted subaerially or at shallow water depths and have therefore witnessed

significant gas loss. However, the alternatives to the plume model proposed by

Anderson (1998), propagating fractures and lithospheric edge effects, donot apply

well to the YSRP system, so we consider the origin of the YSRP best explainedby

mantle plume theory.

The origin of the HLP trend is more controversial. In additionto the model

of Draper (1991) involving asthenospheric drag of mantle plume material,there are

three other models: the evolution ofa back arc setting in response to steepening of

the subducted plate (Carlson and Hart, 1987); propagation of riftsor shear zones

within the lithosphere (Christiansen and McKee, 1978; Chnstiansen, 1993); and the

ascent of asthenosphere, moving westward in the subduction counterflow cell, at

the western margin of the spreading of the buoyant residuum of Steens Mountain

and CRB magmatism (Humphreys and others, 2000).

High 3He/4He ratios for the YSRP and CRB contrast with values

determined for Late Tertiary and Quaterriary rocks elsewhere in thewestern U.S.

(Fig. 3.1). If there is a direct material link between YSRP and HLP magmatism, it

shouldbe detectable in the 3He/4He signal. We have determined the 3He/4He of

HLP basalts to test this proposed link. Helium isotope systematicsmay also bear on the origin of the HLP independent of theany relationship to the YSRP. BASALTS OF THE HIGH LAVA PLAINS

Late Miocene and younger volcanic rocks of the High Lava Plainsare

mainly basalts and rhyolites, locally intercalated with volcaniclastic sediments

(Walker and others, 1967; Greene and others, 1972; MacLeod and others, 1992).

Basalts of the HLP were erupted as cindercones and lava flows, commonly

resulting in the formation of overlapping shield volcanoes.

Although compositionally more diverse than often described, most HLP

basalts can be classified as 'high-alumina olivine tholeiite' (HAOT of Hart and

others, 1984). HAOTs crop out widely in the northwestern U.S., including the

HLP, Owyhee Plateau, the Cascades, and the adjacent northern Basin and Range

(Bailey and Conrey, 1992; Bacon and others, 1997; Conrey and others, 1997).

Previous workers have noted that HAOTs compositionally resemble mid-ocean

ridge basalts (MORB) and back-arc basin basalts, but that HAOTsare more

enriched in incompatible trace elements. Review of 171 chemical analyses of HLP

basalts reveals that they are indeed generally primitive (67% Mg#>60), high-

alumina (80% A1203>16 wt%), olivine-tholeiites (70% hypersthene- and olivine-

normative). All HLP basalts are enriched in incompatible trace elements, especially

Ba, Pb, and Sr, with even the most primitive samples having Ba of 60-150ppm

(Draper, 1991; Jordan and others, in prep. [Chapter 4]). Vu]

METHODS

Eighteen olivine-phyric samples were chosen fromacross the High Lava

Plains for 3He/4He analysis. These sampleswere selected to provide thorough

spatial coverage of the HLP, and to investigate temporal variation in several

locations. A sample from Jordan Craters, on the Owyhee Plateau between the HLP

and YSRP, was also analyzed. The bulk composition of analyzed samples spanned

the range of HLP basalts including primitive and evolved basalts, and basaltic

andesites. Samples were crushed, pulverized, and sieved to isolate the 0.25-0.85

mm fraction. A hand-magnet was used to remove the bulk of the groundmass, and

olivine grains were handpicked from the remaining fraction. Sampleswere

ultrasonically cleaned in deionized water and acetone, and air-dried. Helium isotope analyses were performed following standard procedures (Graham and

others, 1998).

RESULTS

Basalts of the High Lava Plains have 3He/4He ratios near 9RA,at the upper end of the mid-ocean ridge basalt (MORB) range (Table 2.1). The only exception is

Newberry Volcano at the western end of the HLP, which has 3He/4He of 7.6-8.0

RA.Of nineteen samples analyzed, only seven produced results that can be interpreted with confidence, due to the extremely low He contents of many samples from this region. In general, olivine from HLP basalts was found to contain relatively low concentrations of trapped helium (0.1-23 ncc/g). The highest helium 71

Table 3.1 Helium Isotope Determinations

Sample Locality Weight3HeI4He ± IHel %Blank Corrections (mg) (R/Ra) (in)(nccSTP/p) °He 41-le ReltableMaomaMResults 21WHLP97 PotHolesLava 347.38.960.22 3.55 5.8 15.6 29WHLP98 S. Flank Newberry 324.97.960.20 2.92 4.8 22.2 3OWHLP9B Green Butte 317.98.76 0.14 10.9 1.1 6.0 43WHLP98 E.FlankNewberry 426.07.590.16 6.03 1.1 11.6 85WHLP98 FourCratersLava 228.48.83 0.11 10.9 1.9 8.5 92-OR-Ol Jordan Craters 299.39.21 0.10 215 0.1 0.8 MammalResults HLP-98-38 DiamondCraters 140.9 9.00 0.96 1.26 21.2 59.8 HLP-98-38 368.0 9.42 0.58 0.64 20.6 60.3 HLP-98-38(Wtd.Mean) 9.31 0.50 HLP-98-33 N. of Jackass Butte 333.6 22.4 1.03 0.75 5.7 46.6 HLP-98-33b 310.9 30.1 1.60 0.65 1.9 59.1 HLP-98-33b 2nd 310.9 68.7 3.14 0.40 1.3 70.2 HLP-98-33b fusedt 190.1 204 2.18 22.7 0.4 13.3 Note: All analyses performed on olivine mineral separates.Gas extractionsperformedby in vacuo crushing except where indicated. 4Heline blanks were run beforeeach sample analysis. Themean blankover the course of these analyseswas 0.1 nccSTP 4He. 2nd=second crushing of same aliquot of sample. t fraction of powder from crushed sample, extraction by fusion at 1800 °C in a resistively-heated furnace.

122° 1200 118° Bend 0 0 t 50Km .7.6 1 Newberry_-. 2 2 0 Burns Volcano 8.O 9.i° ° ' 14 s, '# (/8.8 0 . Jordan 887 , oo' Craters 0 3He/4He (R4) analysis ( (. o9.3 9.2k / Diamond ' 0 Unsuccessful 3He/4He analysis / i Craters Rhyolite Domes Pliocene and Younger Basalts lsochrons of Silicic Volcanism I /

Figure 3.2. Map of the High Lava Plains showing helium isotope determinations from this study. Also shown are Basin and Range normal faults (dark lines), the distribution of Pliocene and younger basalts, rhyolite domes, and isochrons of migrating silicic volcanism (after MacLeod and others, 1975; with ages in Ma). 72

concentration (215 ncc/g) occurs in the sample from Jordan Craters. Samples containing less than 0.7 ncc/g produced varying 3He/4He results, with large uncertainties due to poor ion counting statistics on the 3He beam, and large 4He blank corrections, typically >60%. Some of these samples with low helium concentrations also showed high 3He/4He ratios. This effect appears to be due toa proportionally larger influence of cosmogenic 3He that contaminates the helium released during crushing. Cosmogenic 3He is produced by spallation during surface exposure (Kurz, 1986). It is generally not observed in young samples that are analyzed by crushing, because it is mostly confined to the mineral lattice where it can be released only by melting. Twelve of the samples studied here are Quaternary in age, including all seven that provided meaningful 3He/4He results. None of the seven Tertiary samples produced significant results that can be interpreted confidently in terms of magmatic 3He/4He value; thereby eliminating the possibility of resolving any temporal variations. Lava composition (Table 2.2) appears not to have been a factor controlling helium concentration, as samples successfully analyzed included primitive basalts (21WHLP97, 92-OR-Ol, and

HLP-98-38), evolved basalts (43WHLP98 and 85WHLP98) and basaltic andesites

(29W1HLP98 and 3OWHILP98). There are also no obvious petrographic characteristics that allow a prediction of the concentration of He in olivine from a given sample. 73

Table 3.2. Major and Trace Element Composition of Successfully Analyzed Samples

Sample 2IWHLP97 29WHLP98 3OWHLP98 43WHLP98 85WHLP98 HLP9838 Location 14-P Newberry HIP Newberry I-IP HIP Lat. (oN) 43.7488 43.5909 43.5535 43.7241 43.3458 43.0803 Long. (°W) 120.9682 121.1498 121.2917 120.9978 120.6804 118.7357 Major Elements: XRF (wt.%) sio2 49.16 52.10 53.49 49.98 51.02 47.62 Ti02 1.26 0.91 1.09 0.91 1.62 1.13 17.25 16.98 17.59 18.32 17.22 17.81 FeO 9.41 7.67 7,61 7.09 8.78 9.96 0.17 0.13 0.14 0.13 0.16 0.17 MgO 8.74 9.61 6.02 8.18 6.82 8.80 GaD 10.10 8.57 9.26 11.31 9.38 11.34 Na20 3.05 3.23 3.68 2.93 3.69 2.76 KO 0.52 0.62 0.89 0.83 0.95 0.27 p2 0.34 0.17 0.24 0.31 0.38 0.14 Mg# 65.8 72.2 62.1 70.5 61.7 64.7 Trace Elements: ICP-MS (ppm) Sc 29.5 22.2 26.9 26.1 29.9 31.0

V 189 - - 176 201 225 Cr 272 362 149 196 186 189 Co 51.6 51.1 41.0 49.2 53.6 61.5 Ni 151 284 66.9 127 98.1 144 Co 67.6 73.8 65.2 88.5 68.3 105.4 Zn 71.7 64.5 70.3 66.5 80.6 69.5 8.0 9.7 16.1 11.7 13.4 2.6 Sr 334 503 416 938 430 264 V 25.9 16.9 27.1 17.4 30.3 20.3 Zr 110 87.2 127 108 174 73.0 Nb 11.39 6.58 8.13 7.27 17.99 5.33 Sn 0.94 1.10 1.47 0.59 1.51 0.57 0.19 0.32 0.59 0.25 0.32 0.03 Ba 185 252 302 527 300 149 La 10.2 8.4 12.1 21.6 15.8 5.0 Co 25.3 19.8 28.5 49.2 37.0 13.6 Pr 3.42 2.70 3.92 6.55 4.90 2.00 Nd 15.1 11.3 17.0 27.6 21.3 9.08 3.71 2.87 4.07 4.83 4.91 2.42 1.24 0.98 1.25 1.52 1.66 1.06 3.94 2.93 4.33 4,37 5.08 2.95 Tb 0.67 0.50 0.71 060 0.83 0.55 Dy 4.10 2.77 4.47 3,09 5.08 3.46 Ho 0.88 0.58 0.92 0.59 0.99 0.74 Er 2.42 1.64 2.52 1.65 2.78 1.96 Tm 0.41 0.28 0.41 0.30 0,46 0.34 'vb 2.46 1.57 2.50 1.53 2.75 2.10 Lu 0.36 0.25 0.37 0.24 0.40 0.32 Hf 2.41 2.03 3.26 2.71 3.84 1.69 Ta 0.78 1.58 1.35 0.80 2.52 1.34 Pb 2.34 3.37 3.61 4.23 3.35 1.13 Th 0.94 0.77 1.67 2.40 1.59 0.26 U 0.37 0.43 0.64 0.76 0.57 0.12 74

Interpretation of Marginal Results

Two samples with low 4He concentrations, near 0.7 ncc/g,were analyzed in more detail in an attempt to gauge the significance of their crushed 3He/4He. HLP-

98-33 produced a high 3He/4He of 22RAwhen first crushed. If such a high value were truly magmatic, this analysis would provide significant evidence forYSRP influence on HLP magmatism. A second olivine split of HLP-98-33 (b in Table

2.1) was analyzed by crushing in two steps. The first step again produceda high

3He/4He ratio (30.1RA),although this result was outside analytical uncertainty of the initial measurement. A second crushing step showedeven higher 3He/4He, 68.7

± 3.1RAwhich is an unreasonable magmatic value. Melting the crushed powder from this sample then released helium with 3He/4Henear 200RA.These observations confirm that release of cosmogenic 3He is responsible for elevated

3He/4He ratios inour samples with the lowest helium concentrations. The data for this sample, if interpreted at face value, would suggest an exposureage of at least 1

Ma. Exposure for one million years seems plausible considering theage of the sample (7.54 by 40Ar/39Ar; Jordan and others, in prep.), the arid climate, and the possibility for prolonged exposure in the interval following emplacement as well as upon erosional exposure. Contamination of trapped helium by cosmogenic helium affects only samples with very low trapped helium concentration, but should be carefully considered in all such cases. 75

HLP-98-38 from Diamond Craters also had a relatively low concentration of trapped helium. However, crushing ofa second aliquot reproduced the original result withinicTuncertainty (9.00 ± 0.96 and 9.42 ± 0.58RA).Two other considerations support the interpretation of the measured 3He/4He in HLP-98-38as a magmatic value: (1) it was collected from a shielded location in a late Quaternary flow; and (2) it is consistent with our other results from the HLP and Jordan

Craters. We report the weighted mean of the two analyses of HLP-98-38 (9.31±

0.50RA)as the best estimate of the helium isotope composition of this sample

(Table 2.1).

High Lava Plains Helium Isotope Composition: Summary

All of the samples which produced meaningful results are Quatemary in age. Three samples from the western HLP show 3He/4He of 8.8-9.0RA.A sample from Diamond Craters (HLP-98-38) from the eastern HLP is somewhat higher at

9.3RAbut, with a larger uncertainty (± 0.5RAat la), overlaps values from the west. The sample from Jordan Craters (92-OR-Ol), had the highest trapped helium concentration and has 3He/4He of 9.2 ± 0.1 RA. The result for this sample contrasts with a value of 14.8RAreported by Craig (1997) for a sample from "just west of

Jordan Valley" (Figs. 3.1 and 3.3) although the two analyses may be for different units. 76

16 Yellowstone- W. ofn Snake River Plain Jordan Valley

Ici) High ?:Columbia Lava River Medicine Basalts ilOci) Lake Plains / 'jorcian Craters El Newberry Cascades 6 -1- 1 23 121 119 117 115 113 111 Longitude (°W)

Figure 3.3. Plot of helium isotope determinations (±1uncertainty) versus longitude. Fields indicate ranges of previous determinations. Cascades data includes Cerling and Craig(1994),Liccardi and other(1999),and Poreda and Craig (1989).Columbia River basalt data from Dodson and others(1997)projected to higher 3He/4He, as they interpret the initial 3He/4He to be as high as 20RA.West of Jordan Valley data from Craig(1997),Medicine Lake Volcano data from Cerling and Craig(1994)and Craig(1997).

Two samples from Newberry Volcano yielded 3He/4He of7.6and8.0 RA.

These values are distinct from those in the rest of the HLP, and fall within the range observed for the Cascade Range to the west(7.1-8.4 RA).Significantly, Newberry

Volcano lies 60 km east of the main axis of the Cascade Range, and shares characteristics with both provinces. From a helium isotope perspective, Newberry

Volcano appears more closely related to the Cascades than to the HLP. This relationship contrasts with that observed in the southern Cascades where Medicine

Lake Volcano occupies a similar position behind the Cascade arc but is 77

characterized by higher 3He/4He (8.9-9.9RA;Cerling and Craig, 1994; Craig,

1997). It is probably best to consider both of these volcanoesas reflecting the

interaction between magmatic sources for the Cascades and Basin and Range/HLP.

ORIGIN OF THE HIGH LAVA PLAINS HELIUM SIGNAL

The 3He/4He ratio of -9RAfor basalts of the HLP is within, though near

the upper limit of, the range (8 ±1 RA)commonly given for MORB unaffected by

mantle plumes (Farley and Neroda, 1998). Anderson (2000) pointedout that this

narrow MORB range is based on a data set excluding high 3He/4He values, and

that there is some circularity in this approach. By considering all data, Anderson

(2000) reported an estimate of MORB 3He/4He of 9.14± 3.59RA.The criticism of

Anderson (2000) is somewhat valid, although there is independent evidenceto consider many high-3He/4He ridge sitesas possibly related to hotspots, and therefore exclusion of them in an attempt to document the "background" MORB helium isotope composition is reasonable. A refined estimate basedon samples from ocean ridges (excluding backarcs and seamounts) and using only a single value at each location is 3He/4He= 8.58 ± 1.81 (1 sd) (D. Graham personal communication).

Previous workers studying Middle Miocene and younger volcanism in the northwestern U.S. have identified three mantle components contributing to basaltic magmatism. In the usage of Carlson and Hart (1987; 1988) theseare: Cl, a depleted MORB-like component, perhaps slightly more isotopically enriched than MORB; C2, a somewhat more evolvedcomponent, although still more depleted

than bulk-earth in Sr-Nd isotopicspace; and C3 an isotopically enriched

component. Different workers have interpreted these components in differentways.

Most controversial is the origin of C2. Carlson and Hart (1987; 1988)interpreted

C2 to be young arc lithosphere, interpretedas depleted mantle (MORB-like)

modified by interactions witha subduction component since the Mesozoic. On the

basis of osmium isotopic compositions, Hart and others (1997) argued thatC2 (and

C3) must be lithospheric. Hooper (1997) and Brandon and Goles(1995) interpreted

C2 as derived from material withina mantle plume.

All workers interpret HAOT, of the HLP and elsewhere,to primarily reflect

a Cl source, with minor additions of C2 and C3. The helium isotope data presented

here are consistent with dominance ofa MORB (Cl) component in the genesis of

HLP basaltic magmas. Primitive HLP basalts show systematic spatialvariation in the degree of isotopic enrichment from 87Sr/86Sr of 0.7031 andENdof +6.7 in the west to 87Sr/86Sr of 0.705 1ENdof +1.6 in the east (Hart, 1985; Chapter 4). This requires that the proportion of C2 and C3 varies spatially. Both the C2 and C3 sources would be expected to have low 3He/4He because they would have elevated

U and Th concentrations. The precise value of 3He/4He would dependupon the helium concentration, (U+Th)I 3He, and time since enrichment. Low 3He/4He characterizes Precambrian lithosphere elsewhere in the western U.S. (Reid and

Graham, 1996; Dodson and others, 1998). If the HLP He isotope signal is interpreted as derived from a MORB-like asthenosphericsource, the relatively 79

enriched components C2 and C3 must havevery low helium concentrations,

otherwise the HLP 3He/4He would be much lower and spatiallyvariable. The basic

objection to a MORB-like source for the origin of the HLP helium signalis that

most MORB with such values (- 9 R,) are from strongly depletedsources showing

extremely non-radiogenic Sr and Nd isotopic ratios and depletedtrace element

ratios (e.g. La/Sm) (e.g. Graham and others, 1992; Graham and Lupton, 1992;

Lupton and others, 1993).There is no other geochemical evidence that such a

source predominates beneath the western U.S., and it seems unlikely that sucha

reservoir has persisted, uncontaminated, in this back arc-like setting.

Another possible explanation for 3He/4He of -9RAwould be the

widespread addition of helium froma high-3He/4He source, such as a mantle plume. The possibility that C2 is derived froma mantle plume is allowed by the

HLP helium isotope data. Plume-derived helium could balance contributions froma low-3He/4He lithosphencsource, though if the lithosphere were a significant contributor to the helium budget there should be spatial variability in 3He/4He. If voluminous Middle Miocene magmatismwere interpreted as the result of emplacement of a plume head (e.g. Hooper, 1997; Brandon and Goles, 1988;1995;

Dodson and others, 1997), then such a plume head would probably have been emplaced under the base of the lithosphere across an area at least 1000 km in diameter. To have encompassed the HLP and Medicine Lake Volcano (where high

3He/4He is also observed), sucha plume head would require a radius of as little as

550 km (Fig. 3.4). The effects of this plume headmay have been muted or negligible where emplaced under thicker lithosphere, though Anders and Saltzman

(1999) recognize a Middle Miocene deformational event in southern Idaho that

they interpret to reflect the emplacement ofa flattened plume head. There is no

petrologic evidence for a plume component contributing to magmatism in therest

of the encircled area in Figure 3.4, thoughsome workers (e.g. Parsons and others,

1994; Saltus and Thompson, 1995) considera mantle plume as potentially partially

responsible for extension in the northern Basin and Range. Globally,some plumes

emplaced under Precambrian lithosphere hadmore uniform widespread effects (e.g.

Karoo, Parana, North Atlantic Igneous Province), but thesewere also larger more

productive plumes.

IMPLICATIONS FOR GENESIS OF THE HIGH LAVA PLAINS AND RELATIONSHIP TO THE YELLOWSTONE-SNAKE RIVER PLAIN SYSTEM

Although the origin of the FILP helium isotope signature remains unresolved, we can consider the implications of these results for models proposed to explain HLP magmatism, particularly the apparent migration of silicic volcanism. Four models have been proposed to explain HLP magmatism: backarc processes, propagating shear zones, spreading of the buoyant residuum of large igneous province magmatism, and westward drag of plume head material by asthenospheric counter flow. The plume head entrainment model (Draper, 1991) is inconsistent with the current understanding of the dynamics of plume heads as they approach the lithosphere (Griffiths and Campbell, 1991), and are emplaced across E:J1

Thin lithosphere, but little extension: [amatism only at craton margin

( / 450

Thick lithosphere: little manifestation of plume head

Thin lithosphere, undergoing 400 extension: plume head emplacemen drives lithospheric magmatism

/

\\ \\g\N 200 km

\\\

120° 115° 1100

Figure 3.4. Map showing the extent of a symmetric Yellowstone plume head with a radius of 650 km at the time of emplacement (-.17 Ma) (to reach across the HLP and to Medicine Lake Volcano), and regions of different lithosphere and extensional history relevant to subsequent magma genesis. The star indicates the inferred position of plume center at 17 Ma based on maximum plate velocity estimate (Gripp and Gordon, 1990) plus extension (Rodgers and others, 1994), and YS is Yellowstone. Dashed lines indicate approximate positions of the Sr-isotope discontinuities (after synthesis of Ernst, 1988); the 0.706 line is thought to broadly delineate the craton margin.

areas as large as 2,000 km diameter in periods of less than two million years

(Saunders and others, 1997). Jordan and others (2000) have proposed a revision to this model in which the flattened plume head can cause migration of crustal magmatism away from the center of the plume head due to radial decreases in heat

and mass input. That this effect was limited to the HLP and northwestern Basin and Range could be explained by this relatively small plume driving crustal magmatism

only where the lithosphere was relatively thin and undergoing extension.

Of the proposed models, only one is in clear conflict with the helium data

presented above. In its simplest form, the model of Humphreys and others (2000)

suggests that the HLP and YSRP share a common source (asthenospheric). The

contrast between 3He/4He of HLP basalts reported here and helium data previously

reported for the YSRP demonstrates that these provinces do not sharea single common source. Perhaps an additional component, different under the HLP and

YSRP, could be invoked to explain the difference in 3He/4He. The likely second

source would be the lithospheric mantle. However, the Precambrian lithospheric mantle underlying the YSRP would, prior to interacting with plume derived melts, have been characterized by low 3He/4He like Precambrian lithosphenc mantle under other parts of the western U.S. (Reid and Graham, 1996; Dodson and others,

1998).

The other models remain permissible in light of the helium data presented here. There are some inconstancies, summarized briefly here, with other aspects of several of these models. Regarding the propagating shear zones model

(Christiansen and McKee, 1976; Christiansen, 1993), faulting in the HLP province is of very low magnitude and appears not to have propagated on the relevant time scale. Regarding the back-arc model (Carlson and Hart, 1987), it is not clear that significant changes in the geometry of the subducting slab have occurred on the relevant time scale; and the amount of extension inferred to have occurred in the HLP area on the basis of paleomagnetic studies in the Coast Range (e.g. Magill and

Cox, 1980) at the time this model was publishedwas too high (Wells and Heller,

1988). We find other evidence supportinga mantle plume interpretation for the

YSRP and a plume head interpretation for the Steens/CRB event compelling, and

therefore believe a plume head may also have playeda role, along with preexisting

lithospheric structure and lithospheric deformation, in the genesis of the High Lava

Plains province.

CONCLUSION

Helium isotope analysis of basalts of the Oregon High Lava Plains have been used to test for a relationship between the High Lava Plains and the

Yellowstone-Snake River Plain magmatic system to the east. Two fundamental

observations emerge: (1) the basalts of the HLP have 3He/4He near theupper end of the MORB range (3He/4He= 9RA);and (2) the helium isotope composition of basalts from Newberry Volcano (7.6-8.0RA)indicate its affinity with the Cascade magmatic province. MORB-like 3He/4He suggests that HLP basalts were derived from source similar to the MORB source. However, enriched trace element signatures, and variably enriched isotopic signatures require a more complex multicomponent model. Both plume and non-plume models seem feasible to explain HLP isotopic and trace element characteristics of HLP basalts. We tentatively prefer a model in which the 3He/4He results and migrating silicic volcanism are explained by emplacement of a portion of a flattened plume head under thin extending lithosphere in southeastern Oregon. Inany case, given the current state of understanding of the two provinces, the existence of the High Lava

Plains trend should not be considered evidence for, or against, a mantle plume origin for the Yellowstone-Snake River Plain trend.

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Walker, G.W., Peterson, N.Y., and Greene, R.C., 1967, Reconnaissance geologic map of the east half of the Crescent Quadrangle, Lake, Deschutes, and Crook Counties, Oregon: U.S. Geological Survey Miscellaneous Investigations Map I- 457, scale 1:250,000.

Wells, R.E., and Heller, P.L., 1988, The relative contribution of accretion, shear, and extension to tectonic rotation in the Pacific Northwest: Geological Society of America Bulletin, v. 110,p. 325-338. CHAPTER 4

BASALTIC VOLCANISM OF THE OREGON HIGH LAVA PLAINS

Brennan T. Jordan'

Anita L. Grunder'

Bruce K.Nelson3

David W.Graham2

Robert A.Duncan2

of Geosciences, Oregon State University, Corvallis, OR 97331

2College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331

2Department of Geological Sciences, University of Washington, Seattle, WA 98195

for submission to Geological SocietyofAmerica Bulletin 91

ABSTRACT

The High Lava Plains province (HLP) of central and southeastern Oregon is

a late Cenozoic bimodal volcanic field at the northwestern margin of the Basin and

Range province. Basaltic rocks of the HLPare mostly primitive high-alumina

olivine tholeiites, with subordinate calc-alkaline and alkali basalts, basaltic

andesites, and basaltic trachyandesites. The most primitive HLP basalts show

exhibit some variability in FeO*, Na20, and CaO suggesting derivation by partial

melting in the mantle at depths ranging from 35to 65 km. Major element variation

of HLP basalts is consistent with models of nearly simultaneous fractionation of

plagioclase, clinopyroxene, and olivine with assimilation becoming significant below 7 wt% MgO. The crystallizing assemblage restricts the crystallization pressures to 1.5-3.0 kb (5-11 km). All HLP basalts are enriched in incompatible trace elements with respect to MORB, with pronounced enrichments in the fluid- mobile elements Ba, Sr, and Pb. HLP basaltsare also isotopically enriched relative to MORB with 87Sr/86Sr of 0.70305 to 0.70508 andENdof +6.7 to +1.6. Isotope and some trace element (e.g. Zr/Nb) systematics of Pliocene and Quaternary basalts vary spatially across the HLP with a discontinuity at about 119.5 °W. Miocene basalts of the HLP are isotopically similar to Middle Miocene basalts immediately east and north of the HLP, and do not reveal the 119.5OW discontinuity. Variation in trace element ratios of primitive HLP basalts suggests that their source was predominantly depleted upper mantle (similar to the MORB-source), with lesser primitive mantle (OIB-source) and subduction components. The interpretation of 92

an OIB component in the HLP basalt source is consistent with helium isotope data

suggesting the possibility of broadly dispersed mantle plume material under the

HLP. We suggest that plume-relatedprocesses were probably critical in genesis of

the High Lava Plains volcanic field.

INTRODUCTION

Late Tertiary and Quaternary volcanism near the northern margin of the

Basin and Range province of the western United States has focusedon two trends

characterized by migrating silicic volcanism: the Yellowstone Plateau-Snake River

Plain system (YSRP) of Idaho and Wyoming, and the High Lava Plains province

(HLP) of southeast Oregon (Fig. 4.1). These trends co-originate in the Oregon-

Idaho-Nevada border area, and crudely mirrorone another, the YSRP younging to

the northeast, and the HLP younging to the west-northwest.

The YSRP trend is widely interpreted to reflect southwestward motion of

the North American plate overa stationary mantle plume (e.g. Armstrong and

others, 1975; Pierce and Morgan, 1992; and Smith and Braile, 1994). Some

workers contest this interpretation citing two lines of evidence contradicting the mantle plume hypothesis for the YSRP: (1) the inconsistency between the track length and plate motion estimates, especially prior to 10 Ma (Fig. 4.1); and (2) the existence of the apparently related HLP trend, clearly not of a simple mantle plume origin (e.g. Hamilton, 1989; Christiansen, 1993). The origin of the HLP trend is particularlyenigmatic. Christiansen (1993) proposed that the HLP trend is the result 93

of a propagating shear zone accommodating the northward termination of Basin and Range extension. Carlson and Hart (1987) related Middle Miocene magmatism and subsequent propagation of HLP silicic volcanism to the back arc setting, and a change in the geometry of subduction. Draper (1991) proposed that the HLP trend reflects the entrainment of plume head material in a subduction induced asthenospheric counter flow cell. Humphreys and others (2000) refined this model, proposing that both the HLP and YSRP trends could result from mantle flow around the buoyant residuum of the Middle Miocene magmatic event (whatever its origin) in the shear fields created by plate motion and counter flow.

We have determined the major- and trace element composition and isotopic composition of HLP basalts in order to document the genesis and evolution of basaltic magmas of the HLP. Synthesizing these observations with other regional petrologic and structural observations we interpret the processes responsible for the genesis of migrating silicic volcanism of the HLP, as well as Columbia

River/Steens Basalts, and the YRSP trend.

Tectonic Setting

The High Lava Plains province lies at the margins of four provinces of distinct tectonic origin, each of which has potential bearing on the origin of the

HLP: the Cascade Range, the Basin and Range province, the Owyhee Plateau, and the Blue Mountains/Columbia Plateau (Fig. 4.1). The Cascade Range lies immediately west of the HLP and is an active volcanic arc, generated by 94

A

A J I 3''_o1 '1' A A ,__ijJ \\ ) r I A CRB / ) ) ) .' 'h lava 1/ PIaj <

cS[ A

I NNRI\ 100km

1300 125° 120° 115° 110°

Figure 4.1. Map showing the tectonic setting of the Oregon High Lava Plains and Snake River Plain. OP=Owyhee Plateau, Y=Yellowstone, NV=Newberry Volcano, M=McDermitt Caldera. Pliocene and younger basalts of the HLP and YSRP are shaded gray. The bold dash-dot line shows the limit of Basin and Range extension. Curved lines cutting across the HLP and northwestern Basin and range are isochrons of silicic volcanism, 10 Ma and 1 Ma are labeled. Encircled areas are caldera complexes of the YSRP and Owyhee region (after Pierce and Morgan, 1992); ages are given for some calderas to indicate age progression. Also shown are dike complexes which fed Middle Miocene flood basalts; CRB, Columbia River basalt dikes; SB, Steens Basalt dikes; NNR, Northern Nevada Rift. Bold stipled lines across the YSRP are projected back from Yellowstone to show the lengths of hotspot tracks predicted by global plate motion models (the northern line is based on Gripp and Gordon, 1990; the southern line is based on MUller and others, 1993). The light dashed lines indicate approximate positions of the 87Sr/86Sr discontinuities (after synthesis of Ernst, 1988); the 0.706 line is thought to broadly delineate the craton margin. subduction of the Juan de Fuca plate under North America at the Cascadia subduction zone. Cascade volcanism has occurred since the late Eocene (-40 Ma).

The current phase of magmatism, the High Cascade episode, began at -7.5 Ma (e.g.

Priest, 1990).

The Basin and Range is a broad region of continental extension, in the western interior of the United States and Mexico. While much of the region within the Basin and Range had undergone a previous phase of extension in the early

Tertiary, the block faulting pattern responsible for the modern Basin and Range topography began around 17 Ma (e.g. Zoback, 1979). The HLP lies at the northwestern margin of the Basin and Range. Apparent displacement on Basin and

Range faults declines steadily northward as the Basin and Range province impinges on the HLP, few Basin and Range faults occur within the HLP. Faulting in the HLP occurs mainly on northwest-trending faults of modest offset (<100 m), constituting the Brothers fault zone. This fault pattern continues into the northern Basin and

Range. Although still a matter of considerable debate, best current models explain most Basin and Range deformation as the result of gravitational collapse of previously thickened lithosphere, with plate margin processes, mantle plume emplacement, and back arc extension, of secondary importance (e.g. Sonder and

Jones, 1999; Humphreys, 2000).

The Owyhee Plateau is largely underlain by Middle Miocene basalts and rhyolite tuffs and lava flows. Rhyolites of the Oywhee Plateau are of the appropriate age 16-12 Ma to represent the southwestward extension of the Yellowstone-Snake River Plain volcanic trend, andare widely interpreted as such

(e.g. Smith and Braile, 1992). However there isno clear pattern of migrating silicic

volcanism within the Owyhee Plateau.

The Blue Mountains province, north of the High Lava Plains, is underlain

by primarily pre-Miocene rocks including earlyto middle Tertiary volcanic and

sedimentary rocks, and Paleozoic and Mesozoic accretedterrane rocks (Valuer and

Brooks, 1986). These rocks and those of the Klamath Mountains southwestof the

HLP probably reflect the basement geology underlying Neogene volcanic rocksof

the HLP. Also widely exposed in the Blue Mountainsare Middle Miocene volcanic

rocks including the Columbia River basalts (CRB), Prineville basalts, and

Strawberry Mountain volcanics. Dikes which fed the eruption of the Columbia

River basalts are exposed in the Monument, Cornucopia, and Chief Joseph dike

swarms in the Blue Mountains (Fig. 4.1). The CRB underlie the Columbia Plateau,

and, combined with the Steens Basalts, constitutea modest sized large igneous

province (-240,000 km3; summed from Tolan and others, 1989 and Carlson and

Hart, 1987).

The origin of the CRB is equivocal. Most workers currently relate them to

the Yellowstone-Snake River Plain trend (e.g. Brandon and Goles, 1988; 1995;

Hooper, 1997; Geist and Richards, 1993; Camp, 1995), perhaps reflecting the interaction between a plume head and the North American plate. A problem with this hypothesis is the off-trend position of the CRB feeder dikes. Several models have been proposed to explain this observation: Thompson and Gibson (1991) 97

proposed that partial melting occurred only where plumematerial could reach

preexisting thin-spots in the lithosphere; Geist and Richards(1993) suggested that

the mantle plume had been trapped under, and deflected northby, the subducted

slab; and Camp (1995) proposed thata plume head was deformed against the

"backstop" of thick cratonic lithospherenear the Oregon-Idaho border.

Alternatively, Smith (1992) suggests that back-arc extensionmay explain this

voluminous magmatic province.

We must consider processes related to regional extension, subduction,and

mantle plumes as potential contributions to the High Lava Plains volcanicprovince.

Previous Studies

The High Lava Plains province and adjacent northern Basin and Range

were mapped at a reconnaissance scale by Walker and Repenning (1965), Walker

and others (1967), Greene and others (1972), and MacLeod and Sherrod (1992).

The regional stratigraphy of the eastern HLPwas described in detail by Walker

(1974). Newberry Volcano and the adjacent western HLPwere mapped in detail by

MacLeod and others (1995).

Waters (1962) described a high-alumina plateau basalt province east of the

Cascade Range in central and southeastern Oregon, extending into northern

California and Nevada. Hart and others (1984) recognized that high-alumina olivine tholeiites (HAOT) were the predominant basalticmagma type across the northwestern Basin and Range province. The trace element composition of HLP 118 121 12O 119 44: irNC L J 2'i>/, . ,,,,,... \4'

__r"°° I,

S ,

< 161 43

______NLate Quaternary Basalt (<4Oka) ] Newberry Volcano Basalt (0 & Late 0) V L LIQuaternary Basalt / k? UPliocene Basalt '. UMiocene Post-Steens Basalt DRhyoirteskl5Ma) ____ ,,4 I

Figure 4.2. Age and distribution of basalts of the High Lava Plains province, after Jordan and others, in prep. (Chapter 2). Also shown are isochrons of silicic volcanism (ages in Ma) after Jordan and others, in prep. (Chapter 2). NC=Newberry Caldera, PH=Pot Holes lava field, DG=Devil's Garden lava field, EL=East lava field, FC=Four Craters lava field, DC=Diamond Craters lava field.

basalts was first described on a regional basis by White and McBirney (1978), as

part of a broader survey of Cascade volcanism. McKee and others (1983) studied

the HAOT of the Devil's Garden lava field of northern Nevada and southeastern

Oregon, and pointed out similarities between HAOT and basalts erupted at mid-

ocean ridges and back arc basins. Draper (1991) focused on the major and trace

element composition of HLP basalts, and recognized the predominance of HAOT

among basalts in the HLP. Brandon (1989) considered the petrogenesis ofbasalts

of the Bear Creek area at the northwestern corner of the HLP, including some Late

Miocene HLP basalts. Bailey and Conrey (1992) noted the presence of HAOT in

some Middle Miocene (-16 Ma) basalts of the Columbia River BasaltGroup (Picture Gorge and Powder River), and that HAOTare also present in the Cascade

Range. HAOT in the Cascade Range were considered in more detail,as one of the mantle contributions to arc volcanism, by Bacon and others (1997) and Conrey and others (1997). Based on these studies the following generalizationscan be made about basalts of the HLP and the HAOT in the adjacent provinces.

(1) Basalts of the HLP are generally primitive olivine tholeiites, similar to

mid-ocean ridge basalts but with higher A1203 (-2 wt%), higher Na20

(-0.5wt%), higher K20(-0.5wt%), and generally lower CaO (-1

wt%) at a given wt% MgO (Fig. 4.4).

(2) HAOT are distinct from high-alumina basalts characteristic of volcanic

arcs (so called HAB), which have high A1203 at moderate to low MgO 6wt%.

(3) HAOT are similar to mid-ocean ridge basalts (MORB) and back arc

basin basalts in major element composition, but are generally enriched

in incompatible trace elements, especially Ba, Sr, and Pb, relative to

(4) HAOT of the northern Basin and Range and tholeiites of the Snake

River Plain show systematic variations in isotopic composition from

east (higher 87Sr/86Sr and lower '43Nd/'44Nd) to west (lower

87Sr/86Sr and higher 143Nd/1Nd).

Some focused petrologic studies have been conducted in the HLP. Russell and Nichols (1987) did a detailed petrologic study of Late Quaternary basalts at 100

Diamond Craters. While focusedon rhyolites, MacLean (1994), Grunder and others

(1995), Streck and Grunder (1999), and Johnson and Grunder (2000)considered the petrologic relationships between basalts and rhyolites of the HLP. Thesestudies show that some trace element characteristics of rhyolites mimic spatially related basalts. Relevant details of previous petrologic interpretations will be considered further in the discussion below.

METHODS

Samples were collected from across the HLP to reflect spatial, temporal and compositional variations. Samples collectedwere as fresh as could be obtained in the field. When necessary, weathered surfaceswere sawn from samples and the cut surfaces were sanded with silicon carbide sandpaper. Sampleswere crushed to pea size in a jaw crusher. Clean fragmentswere hand-selected for analysis. Granular samples were further prepared and analyzed byx-ray fluorescence at the

GeoAnalytical Laboratory at Washington State University for major elements and some trace elements (after Johnson and others, 1999).

Additional trace element data were obtained for 71 samples by quadrupole

ICP-MS analysis in the College of Oceanography at Oregon State University.

Samples were digested by sequential dissolution and precipitation in HF and nitric acid. Instrumental drift was monitored by the use of internal standards (spikes of

Be, In, Re, and Bi) and repeated analysis of the standard BCR-1 every sixth or seventh analysis. Repeated analyses of 2WHLP97 indicate relative precision of 2- 101

8% (1 s.d.) for all elements except Co (9%), V (10%), Cu (12%), and Cs (16%).

For the sixteen elements that were analyzed by both ICP-MS and XRF there is generally good agreement (slopes of 1 and correlation coefficients >0.95 in plots of data by the two techniques) except for the REE, Pb, Th, Y, and Sc. At the relatively low concentrations present in these samples, imprecision in XRF results was anticipated for the REE, Pb, and Th, but the Y and Sc variability is harder to explain. ICP-MS analyses are systematically higher than XRF analyses for both Y and Sc. In the case of Sc, high concentrations by ICP-MS and scatter in the

XRFIICP-MS correlation plot may reflect peak interference by 29Si'60 (Robinson and others, 1999). For elements duplicated by ICP-MS and XRF we generally prefer ICP-MS values, because this method produces more precise results for a wider range of elements. For plots of trace element abundance and ratios we use

XRF data for elements for which both methods appear to be equivalent (e.g. Ba, Sr,

Sc, Zr, Ni) because of the larger XRF data set.

Isotopic compositions of Sr, Nd, and Pb were determined at the University of Washington. Sample preparation and analytical procedures were as described by

Henmann and others (1994) and Nelson (1995). All sample splits run for Pb isotope analysis were leached in HC1 prior to dissolution. Some splits for Sr and Nd isotope analysis were not leached in HC1; several samples were run with and without leaching and produced equivalent results. FI,

RESULTS

Occurrence

Basalts of the High Lava Plains range in age from Miocene to Recent (Fig.

4.2), and, unlike rhyolites, show no systematic age progression across the province

(Chapter 2). Miocene and Pliocene basalt lavas are generally exposed in fault scarps and erosional valleys and are typically 2-5 m thick and often emplaced in compound lava sequences. Quaternary basalts of the HLP generally occur in lava fields covering -.20 to 100 km2. Individual lava fields were erupted from central vents or vent complexes. Some lava fields (e.g. Four Craters lava field) were fed by multiple vents aligned along fissures. Many lavas have pahoehoe surface morphologies and were inflated during emplacement (Chitwood, 1994). Some

Quaternary eruptive centers constructed small shield volcanoes. Cinder cones are abundant in the western HLP and on the flanks of Newberry Volcano.

Petrography

HLP basalts are texturally varied, but mineralogically relatively uniform.

Most are aphanitic to sparsely porphyritic (<5% phenocrysts). Olivine (up to 3 mm) and plagioclase (up to 10 mm) are the typical phenocrysts occurring together or,

less commonly, alone. Clinopyroxene (to 2 mm) rarely occurs as a phenocryst phase, always occurring with plagioclase and olivine in a few relatively porphyritic

rocks (>10% phenocrysts). In some samples, phenocrysts are massed in 103

glomerophyric clusters. Phenocrysts are typically euhedral and normally zoned.

Some plagioclase phenocrysts are partially resorbed. In most samples olivine phenocrysts are poikilitic with small spinel inclusions.

Diktytaxitic texture (plagioclase network with interstitial voids) occurs in

-50% of HLP basalts. Most diktytaxitic basaltsare also subophitic; and as the groundmass approaches ophitic texture, the diktytaxitic character declines. Several diktytaxitic basalts completely lack clinopyroxene oikocrysts in the groundmass; these have the highest proportion of diktytaxitic voids. Intergranular groundmass texture is common in non-diktytaxitic HLP basalts, consisting of plagioclase, olivine, clinopyroxene, and Fe-Ti oxides. Some HLP basalts have an intersertal texture with a significant proportion of glassy, devitrified, or hypocrystalline groundmass, often with plagioclase microphenocrysts.

Major Element Composition

Representative major element data for High Lava Plains basaltic rocks are presented in table 4.1, the complete data set of 114 new analyses is presented in

Appendix 1. In discussing the composition of HLP basaltic rocks, we also consider

56 analyses reported by previous workers of the 'Oregon State University HLP team': Streck and Grunder (1999), MacLean (1994), Johnson (1995), Johnson

(1998), Johnson and Grunder (2000), and unpublished data of Grunder and Streck.

These additional samples were analyzed by XRF and INAA. 104

Table 4.1. Average and Representative HLP Basalt Compositions

Sample Average Average 138CHLP98 92WHLP98 21WHLP97 148CHLP98 Lat. HLP Basalt Primitive 43.4659 43.5211 43.7488 43.2466 Long. (n=170) (n=10) 119.8200120.7803120.9682119.5299

ApV - - 0 0 M MajorElementsXRF (Weight %) S102 50.61 48.36 48.78 48.26 49.16 48.86 Ti02 1.41 0.89 0.68 1.04 1.26 1.41 A1203 16.95 17.33 18.38 17.61 17.25 16.75 FeO 9.67 9.06 7.62 9.26 9.41 10.34 Iti0 0.18 0.18 0.15 0.18 0.17 0.18 7.10 9.84 9.47 9.21 8.74 8.57 9.71 11.59 12.20 11.57 10.10 9.98 Na20 3.23 2.40 2.44 2.67 3.05 3.02 K20 0.78 0.22 0.17 0.09 0.52 0.58 P205 0.35 0.13 0.10 0.12 0.34 0.31

Mp# 63.2 72.7 75.2 70.8 69.4 66.9 Trace-ElementsXRF(ppm) Sc 31 37 35 40 30 32 V 235 226 171 230 199 257 Cr 166 276 184 225 255 233 Ni 106 188 157 146 157 155 73 90 86 78 64 95 Zn 82 60 48 61 69 79 18 14 14 16 15 20 Pb 11 2 1 8 6 Sr 382 214 176 181 332 320 V 28 23 20 24 24 25 Zr 112 54 49 59 111 93 Nb 7.6 4.5 5.5 2.5 11.0 6.0 Ba 373 122 76 64 168 302 La 11 9 4 5 12 6 Ce 30 11 8 13 27 22 Pb 2 Th 2 1 1 4 3 Trace-ElementsICP-MSt(ppm) Sc (4.5) 31 38 37 40 29 31 V (9.8) 232 236 215 189 246 Cr(7.7) 187 279 212 225 272 242 Co (8.9) 50 53 63 54 52 73 Ni (4.1) 114 180 154 147 151 157 Cu (12.3) 78 82 89 80 68 102 Zn (5.0) 84 61 49 65 72 84 Rb (4.3) 11.7 2.0 1.5 0.5 8.0 6.8 Sr(3.7) 393 227 183.8 180 334 329 V (3.7) 29.1 21.5 19.2 22.7 25.9 27.1 Zr(4,1) 117 58 53 60 110 93 Nb (3.5) 8.5 4,5 4.5 2.7 11.4 7.1 Sn (2.7) 1.03 0.59 0.66 0.38 0.94 0.84 Cs (15.9) 0.3 0.1 0.0 0.2 0.0 Ba(3.8) 401 137 74 63 185 328 La (3.5) 12.3 3.9 3.1 2.7 10.2 8.7 Ce (3.3) 29.2 9.8 8.9 8.0 25.3 22.0 Pr(5.1) 4.1 1.7 1.2 1.3 3.4 3.1 Nd (4.2) 18.5 7.3 5.0 6.7 15.1 14.4 Sm (5.4) 4.4 2.2 1.5 2.2 3.7 3.8 Eu (3.0) 1.50 0.86 0.64 0.98 1.24 1.40 Gd (2.7) 4.6 2.7 2.1 2.9 3.9 4.0 Tb (4.1) 0.77 0.50 0.42 0.56 0.67 0.72 Dy (3.9) 4.7 3.3 2.9 3.6 4.1 4.5 110 (3.7) 0.98 0.73 0.69 0.80 0.88 0.94 Er (3.5) 2.73 2.10 1.98 2.22 2.42 2.60 Tm (3.2) 0.45 0.36 0.35 0.41 0.41 0.45 Yb (5.0) 2.7 2.2 2.3 2.3 2.5 2.5 Lu (4.7) 0.40 0.34 0.34 0.36 0.36 0.36 Hf (2.0) 2.82 1.38 1.14 1.47 2.41 2.24 Ta (7,4) 0.87 0.43 1.67 0.18 0.78 1.63 Pb (4.1) 3.4 1.0 0.7 0.9 2.3 2.3 Th (3.5) 1.11 0.22 0.23 0.09 0.94 0.63 U (6.31 0.45 0.10 0.07 0.05 0.37 0.15 Note:%standard deviation ofICP-MS analyses given inparentheses based on lIve analyses of 2WHLP97. Significant figures shwon are as wouldbe required toexpress uncertainty to one significant figure for most samples. BD=below defectionlimit. 0=Quatemary, P=Pliocene, M=Miocene t averaoespublished and unpublishedinclude INAA data from previous workers cited in text 105

Table 4.1. continued

Sample 8WHLP9785WHLP98 HLP9812 HLP9828 2WHLP97 6WHLP98 Lat. 43.9281 43.3458 43.1261 42.8120 43.9220 43.9229 Long. 121.0051 120.6804120.3898 119.5066 121.0048121.0033 Age* P 0 M M M M Major ElementsXRF(Weight %) Si02 49.37 51.02 52.15 51.28 53.91 56.32 Ti02 1.63 1.62 1.23 1.79 1.24 2.10 A1203 15.81 17.22 17.49 15.22 17.04 14.89 F 9.22 8.78 8.98 11.46 9.16 9.76 MnO 0.16 0.16 0.17 0.18 0.17 0.19 Mg0 8.22 6.82 6.35 5.87 4.84 3.43 10.60 9.38 8.83 9.97 7.61 7.19 Na20 2.67 3.69 3.40 3.16 3.82 3.94 K20 1.72 0.95 1.04 0.79 1.51 1.28 P205 0.60 0.38 0.36 0.28 0.69 0.90

M# 68.5 65.5 63.3 55.6 56.3 46.2 Trace-ElementsXRF(ppm) Sc 33 24 25 40 28 39 V 257 213 219 340 177 210 Cr 332 176 127 146 75 33 Ni 126 91 90 43 47 12 cu 35 58 77 121 43 35 Zn 81 70 84 93 96 103 Ce 19 17 19 20 21 17 Pb 27 13 11 9 15 25 Sr 1199 427 493 288 536 337 V 27 27 26 29 26 50 Zr 195 165 117 105 169 152 Nb 7.1 16.7 6.0 9.2 12.2 9.3 Ba 1449 268 425 369 637 574 La 29 19 22 7 11 13 Ce 66 51 34 12 59 39 Pb 9 1 2 1 1 6 Th 3 2 3 2 4 Trace-Elements ICP-MSt (ppm) Sc (4.5) 33 30 26 42 24 32 V (9.8) 246 201 223 190 Cr (7.7) 323 186 140 145 90.5 29.6 Co (8.9) 70 54 47 40 36 29 Ni (4.1) 128 98 94 47 61.6 19.5 Cu (12.3) 52 68 75 129 55 36 Zn (5.0) 83 81 88 120 99 107 Rb (4.3) 28.0 13.4 12.3 11.0 15.6 27.9 Sr(3.7) 1183 430 513 311 552 356 V (3.7) 28.8 30.3 26.6 32.0 31.2 56.2 Zr(4.l) 170 174 123 119 179 166 Nb (3.5) 8.6 18.0 7.6 9.6 13.6 10.5 Sn (2.7) 1.23 1.51 0.83 1.24 1,24 1.50 Cs (15.9) 0.4 0.3 0.3 0.3 0.3 1.1 Ba (3.8) 1435 300 431 374 667 634 La (3.5) 28.6 15.6 14.3 10.6 25.6 20.6 Ce (3.3) 71.3 37.0 32.5 24.9 57.5 47.3 Pr (5.1) 10.5 4.9 4.4 3.5 7.6 6.8 Nd (4.2) 45.2 21.3 194 16.3 31.8 32.7 Sm (5.4) 8.2 4.9 4.3 4.4 6.6 8.3 Eu (3.0) 2.49 1.66 1.40 1.54 1.84 2.57 Cd (2.7) 6.9 5.1 4.4 4.5 6.0 8.2 Tb (4.1) 0.94 0.83 0.74 0.81 0.90 1.36 Dy (3.9) 5.1 5.1 4.3 4.9 5.2 8.0 Ho (3.7) 0.96 0.99 0.89 1.04 1.02 1.76 Er (3.5) 2.68 2.78 2.42 2.96 2.84 4.88 Tm (3.2) 0.41 0.46 0.43 0.46 0.47 0.78 Yb (5.0) 2.3 2.7 2.4 2.9 2.7 4.5 Lu (4.7) 0.36 0.40 0.36 0.44 0.42 0.70 HI (2.0) 4.93 3.84 2.93 2.94 3.91 4.17 Ta (7.4) 0.99 2.52 0.80 0.56 0.72 0.73 Pb (4.1) 10.6 3.3 4.2 3.5 6.5 8.1 Th (3.5) 2.11 1.59 1.13 1.16 1.13 2.93 U (6.3) 0.90 0.57 0.43 0.47 0.48 1.07 106

Basaltic rocks of the High Lava Plains are dominantly basalts (67%), of which the vast majority are olivine tholeiites and a few are nominally alkali basalts with <2% normative nepheleine (Fig. 4.3). Basaltic andesites make up about 25% of the sampled rocks and the balance (8%) are basaltic trachyandesites; both groups are mainly quartz normative 9Fig. 4.3). 60% of samples have Mg#> 60 (Mg#= 100 x molar-Mg/[Mg+Fe2], assuming molarFe2+fFet= 0.79 based on average of values reported for HAOT in adjacent provinces by McKee and others, 1983 and Bacon and others, 1997), and 85% are aluminum-rich (>16 wt% A1203). The previously applied description of "generally primitive high-alumina olivine-tholeiite" (Draper,

1991) seems to apply, although significant variation outside of this class is recognized.

The distribution of rock types west to east across the HLP is not uniform.

Basaltic andesites and basaltic trachyandesites are more common west of 120 ow

(46% of samples) and uncommon east of 119°w(7% of samples). Rocks plotting in the calcalkaline field of Miyashiro (1974) are more abundant to the west and nepheline-normative rocks are more abundant in the east.

CaO and CaO/ Al203 generally decrease and Na20, K20, and Si02 generally increase with decreasing MgO (Fig. 4.4 and 4.5). A1203, FeO*, and

Ti02 generally covary with MgO at MgO >7.5 wt%, and scatter at MgO <7.5 wt%.

K20 and Si02 are also more scattered at lower MgO. There are some high-K20 outliers at high MgO. Generally, K20 1P205 is low in HLP basalts (85% have 107

Figure 4.3. (following page) Classification plots of HLP basalts. A) JUGS classification after LaBas and others (1986); B) tholeiite-calcalkaline discrimination plot of Miyashiro (1974); and C) the base of the basalt tetrahedron of Yoder and Tilley (1962), plotting CJPW normative nepheline (ne), albite (ab), quartz (q), hypersthene (hy), and olivine (ol), projected from diopside. Highlighted data (red) are the ten 'most-primitive' basalts described in the text. 108

7.0 ED O\ 6.5 6.0 saltic Trachyandesiteon o5.5 ('4 :10 5.0 D 0 + 0 o4.5 rJ 0 4.0

3.5 Basalt Basaltic Andesite 3.0 2.5 A U 2.0 454647484950 51 52 53 54 55 56 5 Si02

58 D 0 56 0 D 0 oD 0 0 0DJ 54 CalcalkahneD 0('4 0 o o Tholeiitic o 0 0 oD0 48 B 0 46

0 1 2 3 4 5 6 FeO/MgO

ne

hy

Figure 4.3 109

K20 1P205 <3), but a few have distinctly high ratios, even at high MgO (Fig. 4.5).

Ti02 and FeO* have generally similar behavior (Fig. 4.5), however Ti02 covaries somewhat with Na20, and FeO* does not. Na20 variation with MgO defines two trends, a high MgO (>7 wt%) trend which projects to higher Na20 than the low

MgO group, which are not obvious when plotted against CaO (Fig. 4.5).

To describe HLP basalts least likely to have been affected by fractionation and assimilation we considered 42 samples (of the 170 sample data set) meeting general criteria for primitive character (Mg# >60, MgO >8 wt%, Ni >140 ppm, Cr

>180 ppm, and K20/P205 <3). Covariation of Mg, Ni, and Na20 among these 42 samples indicates that, despite their primitive character, much of their variability reflects fractionation. A subset of ten of these samples, with MgO > 9.4 wt%, is taken to represent the most primitive HLP basalts (Fig. 4.3-4.5 and 4.7), and the average of these ten samples is presented in table 4.1. In the remainder of the chapter, the set of 42 samples will be referred to as the "primitive" basalts, and the subset of 10 samples will be referred to as the "most primitive" basalts. The average K20 content of the most primitive basalts is 0.22 wt%, while the lowest value measured in an HLP basalt is 0.09 wt%. The most significant variability among these ten samples is in FeO* (7.62-9.92 wt%), CaO (10.91-12.20 wt%),

A1203 (16.23-18.38 wt%), and Na20 (1.95-2.72 wt%) (Fig. 4.4). There is a good negative correlation between CaO and FeO*, but none in MgO versus Ni or MgO versus Na20 Fig. 4.5 and 4.6). 110

5. 0 5 4

4J 5: 3. '.'j 5 0 0 C') C', zC 3.

4: 2

4 .:1

3j

2.

cv,1 j 2J 0 0 1. 0O°D 0 0

1.0

0.5

3.0

.-. 2.5

2.0 0

0 1.5 C) C') 1.0

0.5

0.0

0.70 o 0.65 I cD cv, o 0.60 C') 0.55 1 0 0.50 a) U- 0 0.45

0.40

3 4 5 6 7 8 9 10 11 3 4 5 6 7 8 9 10 11 MgO (wt%) MgO (wt%)

Figure 4.4. Plots of major element concentration and CaO/Al203 versus MgO of HLP basalts. Highlighted data are the ten 'most-primitive' basalts described in the text. Also shown are vectors indicating 10% fractional crystallization of olivine (0), plagioclase (P), and clinopyroxene (C), and 10% assimilation (A) of a low- silica rhyolite. The blue line is the results of a simple model for evolution of HLP basalts involving fractionation of plagioclase, clinopyroxene, and olivine in proportions 50:30:20, with assimilation of low-silica rhyolite after 40% fractionation at r = 0.4. In the model plagioclase varies systematically from An81 to An52, and olivine varies from Fo85 to Fo76. based on limited microprobe analyses of HLP basalts. Open circles on the model show increments of 10% fractionation out to 60%. 111

I 5 0 10 0 o 08Lf) Dn4 0 0 03 r\J z D LRU I U

5 6 7 8 9 10 11 12 13 MgO CaO (wt%) (wt%) 4 14 0 0 -' 3 0 0 0 12

D 10

a) F' U- Do 8 u 1 D DUr 0 I ° !I!! 06 6 7 8 9 10 11 12 1 14 15 5 6 7 8 9 10 11 12 13 FeO* (wt%) CaO (wt%)

4 flDLJDLl -S 3 55 0 LI 0 0 D 0r'j : (I, I 0 0 ],,,,L I ,,,,I,,, I ,,,I,,,, I 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Na20 (wt%) CaO (wt%)

Figure 4.5. Additional major element variation plots. Highlighted data are the ten 'most-primitive' basalts discussed in the text. 112

Trace element Composition

Most HLP basalts fall on a tight trend of decreasing Ni with decreasing

MgO (Fig. 4.6). The outlier at high Ni and high MgO is a Newberry flank lava with abundant olivine phenocrysts, and is also an outlier in major element variation plots

(e.g. the low CaO outlier in Fig. 4.4). The major and trace element composition of this sample is consistent with addition of olivine, by accumulation, to an evolved basaltic magma. Most HLP basalts also lie on a loose trend of decreasing Sc with decreasing MgO, consistent with clinoproxene fractionation.

Incompatible trace element concentrations generally increase with decreasing MgO (Fig. 4.6, Table 4.1), with greater degrees of enrichment of highly

incompatible elements (e.g. Ce) than moderately incompatible elements (e.g. Yb).

The bulk of the data lie along simple enrichment trends in plots of Ce, Zr, Rb, and

Ba versus MgO. Sr is more complex with more scatter below 7 wt% MgO, and low

Sr at low MgO (<4 wt%). A number samples stand out as outliers in variation plots

involving incompatible trace elements (Fig. 4.6). Seven samples have extreme

enrichments in Ba (>1000 ppm; Figs. 4.6 and 4.7). Five of these samples are from

the central High Lava Plains and are characterized by low MgO (<3.5 wt%) and

'normal' Sr concentrations (200-300 ppm). The enrichment of these rocks has been

interpreted by MacLean (1994) and Streck and Grunder (1999) to reflect many

cycles of fractionation and recharge. Two samples (8WHLP97 & 128 WHLP98)

with extreme Ba concentrations are different in that they have high MgO (>8.0

wt%) and are strongly enriched in Sr (>900 ppm). Note that these two samples are 113

300 0 250 80C 70C 200 E E 60C a 0 350 a SOC 150 40C z 0 o 30C 100 20C 50 1 OC 0

45 0 120' A 00 40 0 0 100' aE 35 80' a 30 a 601 0 25 o 0 0 40'

: 20 201 0

I 15 I I I' 12 0 0

10 0 aE 0 a 8 0 L o o 0 6 0 ..D >- 0 0 2( Qi 4

2 1( 00

C

1 60 2501 0 140 120 200 100 a 0 0 a iso 0 0 80 0 U 60 100 40 o so 20

I I I! 2 3 4 5 6 7 8 9 10 11 2 3 4 5 6 7 8 9 10 11 MgO (wt%) MgO (wt%)

Figure 4.6. Trace elements plotted against MgO. Symbols as in Fig. 4.4. 114

1000

HLP-98-47 A Average HLP Low-Silica Rhyolite HLP-98-25 -.' 131 WHLP98 0) I-ILP-98-60 -. 100 HLP-98-22 138CHLP98 cr O2WHLP9B / / 0 / / Range of 71 HLP Basalt s 10 c:L()

cri

0.11 i I I I I I I I I I I I I I I I Rb Ba Th U Nb Ta La Ce Pb Pr Sr Nd Zr Hf Sm Eu Dy Y Ho Yb Lu

100 r1

0)

10 0 0

(I) 1.0 C3

La Ce Pr Nd Sm Eu Gd TbDy HoEr Tm Yb Lu

Figure 4.7. Field of trace element composition of 1-ILP basalts presented in MORB- normalized incompatible-element spider diagram (A), and a MORB-normalized rare-earth element diagram (B). In both diagrams, elements to the left are more incompatible in basaltic compositions. The normalizing MORB and the order of elements in A are from Sun and McDonough (1989). Six of the ten "most primitive" group were analyzed by ICP-MS and are shown with colored traces on this plot; 92W1-1LP98 is also show because it has some of the lowest incompatible element concentrations. 115

not enriched in Yb, and therefore have very high Ce/Yb (>30). These samples, and

a related but more evolved basalt (high Ba at -6.5 wt% MgO), are all from the

northwestern HLP and are the only HLP basalts with abundant clinopyroxene

phenocrysts.

The incompatible trace element enrichment of HLP basalts generally increases with increasing incompatibility, with distinct enrichments in Sr, Pb, and

Ba (Fig. 4.7). The most primitive basalts are slightly depleted with respect to

MORB (Sun and McDonough, 1989) in Y and the HREE (Fig. 4.7). While the most primitive HLP basalts are similar in many incompatible trace element characteristics to N-MORB of Sun and McDonough (1989) it should be recognized that these HLP basalts have greater Ni (-190 ppm) and are more primitive than the normalizing MORB. Therefore HLP basalts are enriched relative to MORB of similar primitive composition.

Ba is the element most strikingly enriched in the most primitive HLP basalts with an average of near twenty times the MORB value (6.3 ppm). Sr and Pb concentrations in the most primitive HLP basalts are at least double MORB values

(MORB Sr = 90 ppm, Pb = 0.3 ppm).

The REE plot (Fig. 4.6b) of the HLP basalts reveals smooth patterns of enrichment in the LREE. Both modest positive (EuIEu* < 1.37) and negative

(Eu/Eu* > 0.87) Eu anomalies are observed in HLP basalts with an average EuIEu* of 1.00. The most primitive basalts have slightly positive Eu anomalies. Positive Eu anomalies of HAOT in the Cascades have been interpreted to reflect a relatively 116

reduced state of the mantle or residual clinopyroxene in the source (Bacon and others, 1997).

Isotopic Composition

HLP basalts have a considerable range in Sr and Nd isotopes, and a more limited range in Pb isotopes (Table 4.2, Fig. 4.8). 87Sr/86Sr increases with decreasing 143Nd/144Nd (expressed asENd)in HILP basalts, broadly along the mantle array (Fig. 4.8a). Lead isotopes plot on or above the Northern Hemisphere reference line (NHRL) of Hart (1984), like basalts of the northwestern Basin and

Range (Hart, 1985) and Cascade Range (Bacon and others, 1997). The variability in 207Pb/204Pb is quite low, with most samples within 2of the average.

208Pb/204Pb hasa weak correlation with87Sr/86Sr and 143Nd/144Nd, but the other Pb-isotope ratios do not correlate with Sr- or Nd-isotope ratios.

There is no correlation between the degree of evolution of basalts and isotopic ratios (e.g. MgO versus 875r/86Sr; Fig. 4.8 and 4.9), so first order variability in isotopic ratios can not be attributed to assimilation during fractional crystallization. There is no correlation between isotopic ratios and trace element concentrations or ratios. 117

Table 4.2. Isotopic Analyses

Sample Latitude Longitude Rock 143Nd/"4Nd ENd 875r/865r 206Pb/204Pb207Pb/204Pb208Pb/204Pb 8-WHLP-97 43.9281 121.0051 B 0.512874 4.6 0.703738 18.835 15.574 38.439

15-WHLP-98 43.0913 120.8375 B 0.512855 4.2 0.703713 18.828 15.573 38.413

21-WHLP-97 43.7488 120.9682 0.512908 5.3 0.703342 18.925 15.576 38.487

29-WHLP-98 43.5909 121.1498 B 0.512887 4.9 0.703681 18.882 15.575 38.537

30-WHLP-98 43.5535 121.2917 B 0.512904 5.2 0.703651 18.939 15.564 38.512

43-WHLP-98 43.7241 120.9978 0.512858 4.3 0.703753

81-WHLP-98 43.6133 120.6870 B 0.512802 3.2 0.704248 18.999 15.572 38.595

85-WHLP-98 43.3458 120.6804 B 0.512936 5.8 0.703279 18.788 15.588 38.556

92-WHLP-98 43.5211 120.7803 0.512911 5.3 0.703686 18.945 15.590 38.583

131-WHLP-98 43.6547 120.1002 0.512967 6.4 0.703402 18.797 15.576 38.477

138-CHLP-98 43.4659 119.8200 0.512980 6.7 0.703055

148-CHLP-98 43.2466 119.5299 0.512866 4.4 0.703777 18.911 15.587 38.538

HLP-98-22 42.6755 120.0122 FB 0.512922 5.5 0.703680 18.799 15.594 38.470

HLP-98-25 42.5808 119.5988 0.512914 5.4 0.703751 18.848 15.568 38.549

HLP-98-33 43,0570 118.9583 B 0.512807 3.3 0.704120 18.889 15.557 38.470 0. 704120

HLP-98-38 43.0803 118.7357 0.512788 2.9 0.704218 18.876 15.589 38.623

HLP-98-59 43.1397 118.4443 FB 0.512735 1.9 0.704839 18.953 15.608 38.722 0.512735 1.9 0.704837

41-BJ-95 43.6250 120.8700 R 0.512784 2.8 0.704390 19.045 15.599 38.657 * PB=pnmitive basalt, EB=evotved basatt, and RrhyotiIe 118

Figure 4.8. (following page) Plots of isotopic ratios of HLP basalts. Shown are our data (17 basalts [15 in lead isotope plots] and 1 rhyolite), 3 basalts of Hart (1985), 5 basalts of Brandon and Goles (1995), 2 basalts and a rhyolite of Johnson (1995), 1 basalt of Hart and others (1997), and 3 basalts and three rhyolites of A. Grunder and M. Streck, unpublished data. Rhyolite 87Sr/86Sr are initial ratios, corrected for radiogenic in-growth after emplacement. Error bars apply only to new data presented here. Basalts identified as primitive are from our 42 sample data set of primitive basalts, and others analyses meeting the same criteria. All others are labeled as evolved basalts. 119

10,0

90

8.0

7.0

ENd :: A

40

30

20

10

0.0 0 7020 0.7025 0.7030 0.7035 0 7040 0.7045 0 7050 0 7055 0 7060 0 7065

87Sr/86Sr

15630

15620

15.610

. 15.600 0

15.590 B

15580

15. 570

15560

15,550 18750 18800 18850 18900 18950 19000 19050 19100

206pb/204Pb

38.750

38 700

38.650

38.600 0

38.550 C

38.500

38 450

38 400

38. 350 18750 18800 18850 18.900 18950 19.000 19.050 19,100

Figure 4.8 120

Rhyolite 0.706 Evolved Basalt I Primitive Basalt (/) 0.705 U (0 U

. U U (f 0.704 N. U. .11 U .UUU U U .1! U U . 0.703 .

0 2 4 6 8 10 MgO (wt%) rhy. (O.07x) p'. 0.706 U

U 0.705 .

U U.' 0.704 .

U. 0.703 .

III! I I I 0.000 0.005 0.010 0.015 0.020 0.025 (ppm) 8

U U 6 U U . U.. U .0 .U U U

2 U U

0 I I I 0.000 0.005 0.010 0.015 0.020 0.025 1/Nd (ppm)

Figure 4.9. Variation in isotopic ratios with major and trace element composition. Shown are new analyses reported here, as well as previous analyses reported by Johnson (1995), Brandon and Goles (1995; with MgO, Sr, and Nd concentration data from Brandon, 1989) Hart (1997), and unpublished analyses of A. Grunder and M. Streck (with concentration data from MacLean, 1995 and Streck and Grunder, 1999). Basalts are designated primitive or evolved as in Figure 4.8. 121

Spatial and Temporal Variationin HLP Basalt Compositions

Hart (1985) recognized that isotopicratios varied spatially across the

northern Basin and Range, with 87Sr/86Srincreasing and 143NdJ144Nd decreasing

from west to east. Distinctpatterns emerge in spatial variability of 87Sr/86Srand

143N&144Nd, HLPbasalts when Late Miocene basaltsare distinguished from

Pliocene and Quaternary basalts (Fig.4.10). All Late Miocene HLP basalts plot

within the field of Middle Miocenebasalts from units exposed immediatelyeast

and north of the HLP (data fromCarlson and Hart, 1987 and Brandon andGoles,

1995). This field is characterizedby very limited variation in 87Sr/86Sr, and

somewhat greater variability in'43Nd/'44Nd.Pliocene and Quaternary basalts

exhibit more variability in isotopiccomposition. West of about 119.5 °W, Pliocene

and Quaternary basaltsare generally less isotopically evolved (lower 87SrI86Srand

higherENd)and more variable than Middle andLate Miocene basalts. East of

about 119.5 °W, there isa trend of increasing degree of isotopic evolution

eastward, with Pliocene and Quaternarybasalts having more radiogenic Sr than

Middle and Late Miocene basaltseast of 118.5 °W. The divergence of Pliocene and

Quaternary basaltsaway from Miocene basalts in Sr isotopic compositioneast of

-418.5 °W, while remaining concordantwith Miocene basalts in Nd isotopic composition (Fig. 4.10) isa manifestation of the departure of the HLP basalts from the mantle array to elevated 87Sr/86Srin more isotopically evolved samples. In chapter 3 we reported 3He/4He forQuaternary HLP basalts. We found that 122

0

0

0

C/) 0. (0

C,) N- 0

ENd

121° 120° 119' 118° 117° Longitude (°W)

Figure 4.10. Sr and Nd isotopic variation with longitude and age. Plotted are our new data and data from sources cited in Figure 4.8. Shaded areasshow range of Middle Miocene basalts immediately east and north of the HLP based on data from Carlson and Hart (1987) and Brandon and Goles (1995). Basalts are designated primitive or evolved as in Figure 4.8. 123

25 00 0 0 0 P11] 0 20 0 0 o 0 0 0 80 z 0 0 z U C- 0

00 o 10 U

00 0 U U 5. -0

0 DO 0 0 10

2.5 0 Ou o E 8 0 0 o C-) o 0 0 . 0 DD CD 2.0- DO 0 -6 - o -< CD j 0 .D 4 0 0

. 2

0.5- I 0 121 120 119 121 120 119 118 °W Longitude

Figure 4.11 Variation in selected trace element ratios of the set of 42 primitive basalts with longitude. Samples from the subset of ten most primitive basalts are shown with dark symbols.

3HeI4He shows little variationacross the HLP, with a value of -9RA(whereRA = the atmospheric ratio of 1.39 x 10-6). Therefore 3He/4He in Quatemary basalts appears to be decoupled from Sr, and Nd isotopic ratios in these rocks which vary systematically across the HLP.

As discussed earlier, the proportion of basaltic andesites and quartz normative rocks is higher in the west than in the east. However, when comparing rocks of similar degree of evolution (e.g. the 42 samples with Mg# >60, MgO >8 wt%, Ni >140 ppm, Cr >180 ppm, and K20/P205 <3), most major and trace element characteristics show no distinct trends of spatial variation (Fig. 4.11). 124

Some trace element ratios show more diversity in the west than in the east. Grunder and others (1995) recognized that there was spatial variation in Zr/Nb in basalts in the Harney Basin area, with high Zr/Nb to the west. Our broader data set shows that the variation observed near the Harney Basin extends east and west across the HLP

(Fig. 4.11), with an abrupt transition at 119-119.5 °W, separating an envelope extending to high Zr/Nb in the west and a more restricted envelope in the east.

Ratios demonstrating light rare-earth element enrichment (e.g. Ce/Yb and La/Sm) also have different ranges east and west of about 119.5 °W, with much narrower ranges in the east, and ranges extending to higher and lower values to the west (Fig.

4.11). While the change in isotopic compositions at 119.5 ow is observed only in

Pliocene and Quaternary basalts, the spatial variation in Zr/Nb, La/Sm, and Ce/Yb is similar for both Miocene and younger basalts. Some temporal variability is suggested by the observation that 8 of 19 Miocene primitive basalts (from the less restrictive primitive basalt data set of 42 samples) have La/Sm <1.7, but only 1 of

16 Pliocene and Quaternary basalts have La/Sm <1.7 (the totals do not sum to 42 because La and Sm were not determined for all of these samples). No strictly temporal variation is evident in other major or trace element characteristics of HLP basalts. 125

GENESIS OF HIGH LAVA PLAINS BASALTS

Source of Basaltic Magmas

HLP basalts are similar in major element composition to MORB, suggesting similar conditions of melting. By analogy with experiments of Hirose and Kushiro

(1993), HLP basalts appear to be the product of moderate degrees of melting (-10-

30%) of mantle peridotite at 10-15 kb. Bartels and others (1991) performed experiments on an HAOT from Medicine Lake Volcano, similar in composition to primitive HLP basalts, and found it to be in equilibrium with an olivine- orthopyroxene-clinopyroxene-plagioclase-spinel assemblage of at 11 kb. This pressure corresponds with upper mantle depths, just below the base of the crust across the HLP (-37 km; Catchings and Mooney, 1988). Whether equilibration with mantle near the base of the crust reflects melting at this depth or reequilibration of melts derived at greater depths is equivocal. Variable FeO* content (7.62-9.92 wt%) of our most primitive basalts (Fig. 4.4) suggests some variability in the depth; higher FeO at comparable MgO suggests deeper melting

(e.g. Klein and Langmuir, 1987; Hirose and Kushiro, 1993). The suggested pressure difference could be on the order of 10 kb by analogy to the partial melting experiments of Hirose and Kushiro (1993).

Primitive HLP basalt trace element signatures and isotopic characteristics are depleted relative to bulk earth, similarly to MORB, indicating they share a depleted upper mantle origin. The enrichment of many elements, particularly Ba, 126

Sr, and Pb, relative to MORB, however gives proof of other petrologic considerations. We argue that the enrichment of primitive HLP basalts reflects source-enrichment rather than crustal assimilation (e.g. Bailey and Conrey, 1992) based on the following points: (1) even the most primitive HLP basaltsare enriched in Ba by a factor of 10-30 relative to MORB (Fig. 4.7a); (2) HLP basalts have enriched isotopic signatures relative to MORB and there is no correlation between isotopic ratios and fractionation indicators, precluding enrichment by crustal contamination alone (Fig. 4.9); and (3) crustal assimilation, while a factor in the evolution of HLP basalts (see below), does not generate the observed pattern enrichment, assuming that the assimalants were partial melts of wall rock, represented by low-silica rhyoliote (Fig. 4.7a).

The enrichment (relative to MORB) of the HLP basalt source could reflect either the addition of a subduction component or the involvement of an ocean- island basalt (018) source. The greatest enrichment was in the fluid-mobile elements Ba, Sr, and Pb suggesting that subduction metasomatism explains at least part of the enrichment. This enrichment could have been contemporaneous with melting (e.g. flux melting of Reiners and others, 2000) or could have occurred at some time in the past (e.g. Hart and others, 1984). Flux melting (Reiners and others, 2000) is a logical explanation for enrichment in the arc setting, but it is unlikely to have occurred 50-300 km behind the active arc. This interpretation is supported by the lack of a systematic spatial variation in Ba/Nb (Fig. 4.11). The pre-Tertiary basement of the HLP is represented by Paleozoic and Mesozoic 127

accreted terranes of the Blue Mountains to the north and the Klamath Mountainsto the southwest. These terranes include arc terranes (e.g. Valuer and Brooks, 1986), and the post-accretionary period (since --135 Ma) has involved several episodes of subduction related magmatism, so subduction-enriched mantle is likely to be present.

The addition of a subduction component to MORB-source mantle can not explain all of the compositional variation of primitive HLP basalts. There isa negative correlation between La/Sm and Zr/Nb in primitive HLP basalts (Fig.

4.12), inconsistent with variable addition of a subduction component to MORB- mantle which would have produced a positive correlation. This trend could be explained by variable degrees of melting or by variable degrees of mixing of OIB and MORB magmas. Using the extreme primitive Cascade basalt compositions from Medicine Lake and Simcoe Volcano (Bacon and others, 1997) to represent regional MORB and OIB compositions, respectively, La/Sm-Zr/Nb variation of

HLP basalts could be explained by mixing magmas with 2-12% OIB and 98-88%

MORB (Fig. 4.12a). La/Sm-Zr/Nb variation can also be interpreted as the result of variable degrees of partial melting of a mantle consisting of mixed MORB- and

OIB-sources (4. 12b). To explain the range of primitive HLP basalts would require

1-7% melting at a MORB:OIB-source ratio of 70:30 and 2-18% melting at a

MORB:OIB-source ratio of 50:50. Garnet lherzolite and garnet-spine! lherzolite modes were used for these calculations because partial melting of plagioclase- spine! lherzolite produces more limited ranges that can not span the primitive HLP 128

7 7

6 LSR A 6 B \ OIB/MQRB 5 5 \#5%sc (f4E E . (03 S... 018 -J jC3 2 2 U l020 8

0 01d20 0 1 20 30 40 50 60 70 Zr/Nb 0 Zr/Nb

10 8 / OIB/MORB +5%sc

r..j .5.. (0 LSR Sc. 0 U .r 0 . 0 0s0 / 1]5 z10/.. 2 80 0 0 0.05 0.10 0.15 0.20 0.25 °MQRB 0.05 0.10 0.15 0.20 0. Nb/Zr Nb/Li 0.3

LSR E (0.37) 0.2 0

N.J N.J .5.. .5. -o

0.1 0

0 0 0 u.UD u.uu u.0 u.0 U. 0 0.05 0.10 0.15 0.20 0.25 Nb/Zr MOPB Nb/Zr

Figure 4.12 Trace element ratio plots constructed to explore the relative significance of different contributions to the mantle source and the role of varying degrees of partial melting in the genesis of primitive HLP basaltic magmas. Large squares are primitive HLP basalts, with the red being from the ten 'most primitive' basalts described in the text, and the gray being from the other set of 42 primitive analyses described in the text. The number of data points do not sum to 10 and 42 because not all analyses include all of the elements involved in plots; only ICP-MS Nb and Rb data are used in these plots. Small black squares are primitive Cascade basalts from Bacon and others (1997). Partial melting models show incremental batch melting of 1-20%, using subduction component (SC) of Reiners and others (2000), MORB-source of Borg and others (1997), primitive mantle (OIB source) of Sun and McDonough (1989), and partition coefficients of McKenzie and O'nions (1991; 1995). The MORB/OIB-source has equal proportions MORB-source and primitive mantle. ML is Medicine Lake, and SV is Simcoe Volcano of Bacon and others (1997). LSR is low-silica rhyolite computed base on data of MacLean (1994), Johnson and Grunder (2000), and unpublished data of A. Grunder. 129

basalt data at >1% melting. Varying both the proportion of OIB- and MORB- source and the degree of melting would be required to cover the range of HLP basalts with a plagioclase-spinel lherzolite. Increasing the percentage of garnet in the source results in higher La/Sm of low degree melts, but makes little difference at >10% melting.

Mixing MORB and OIB magmas or mantle sources, and varying degrees of melting can explain La/Sm-Zr/Nb variation and Rb/Zr-Nb/Zr variation, but can't explain high Ba/Zr of primitive HLP basalts (Fig. 4.12). Addition of up to 2% subduction component (using the subduction component of Reiners and others,

2000) to a MORB:OIB-source can explain elevated Ba/Zr,. However, addition of more than -0.1% subduction component disrupts the model in La/Sm-Zr/Nb and

Rb/Zr-Nb/Zr space. The discordance between Ba and Rb is a reflection of the high

Ba/Rb (-62) of primitive HLP basalts. To explain elevated Ba/Zr in HLP basalts without disrupting other trace element ratios would require addition of <0.2% subduction component with >3000 ppm Ba (compared with 1500 ppm Ba of

Reiners and others, 2000).

Pliocene and Quaternary basalts are of systematically less evolved isotopic x character (lower 875r/86Sr and higher ENd) from 118 to 119.5 °W, and lack systematic spatial variation west of 119.5°w(Fig. 4.10). Hart (1985) interpreted similar patterns in the northern Basin and Range and Snake River Plain to reflect increasing age of lithospheric mantle from the Mesozoic and Paleozoic accreted 130

terranes in the west to the Precambrian craton to the east. Hart and others (1997)

revisited the problem with Os isotope data, and found the 187os1188os also varies

spatially across the region, leading them to conclude that spatial variations in

isotopic character were the result of both variable addition of a lithospheric component to MORB -like asthenospheric melts and increasing age of this component to the east (up to 2500 Ma). Their limited data set (seven primitive basalts from the 900 km wide area between the Modoc and Yellowstone Plateaus)

showed a strong correlation between Ba and '87Os/'88Os, supporting the interpretation that the proportion of enriched lithospheric component increases eastward. There is no systematic variation in Ba content with space or isotopic ratios in HLP basalts, suggesting that age, rather than amount, of such a component is the primary control on isotopic composition of HLP basalts.

We interpret the spatial variability in isotopic character, and possibly Zr/Nb

and La/Sm variation, of Pliocene and Quaternary HLP basalts to reflect lateral

variations in mantle source characteristics. Miocene HLP basalts show distinctly

less isotopic variability than younger basalts and are identical to Middle Miocene

basalts in 87Sr/86Sr-longitude space (Fig. 4.10), but Miocene HLP basalts exhibit

the same La/Sm-Zr/Nb spatial variations as younger basalts. The existence of a

different pattern of spatial variability in the Miocene than in the Pliocene and

Quaternary could be explained in two ways: (1) Miocene and younger magmas

were derived from different depths, with the Miocene source being more

homogeneous; or (2) there was an influx of material of different isotopic character 131

near the end of the Miocene. At first cut, the more heterogeneous source (Pliocene and Quaternary) could be interpreted as lithospheric, and the more homogeneous source (Miocene) subsublithospheric. However, the difference in proportion of low-LaJSm primitive basalts suggests that Miocene basalts (more low-La/Sm samples) were more frequently derived by either higher degrees of melting, less garnet input, or less OIB source than younger basalts. All of these signals could be interpreted as suggesting generally shallower melting in the Miocene. However, both Miocene and younger primitive basalts have La/Sm that covers the full range of values (1.1-2.7) and the averages are nearly identical (Miocene = 1.98; Pliocene and Quaternary = 2.03). Therefore, the influx of mantle with different characteristics is suggested by these data.

Evolution of Basaltic Magmas

The general patterns of evolution of HLP basalts, as observed in major element variation plots (Figure 4.4), can be accounted for by fractionation alone at

MgO greater than 7 wt%, with some degree of assimilation (ratio of assimilant to fraction crystallized {r] = 0.2-0.5) accompanying fractionation below 7 wt% MgO.

Fractionation of clinopyroxene with olivine, plagioclase is required fairly early in the evolution of HLP basaltic magmas in order to account for the covariation of Sc and CaO/Al203 (Fig. 4.13). The proportion of clinopyroxene fractionation appears to be as great as 0.32 even though clinopyroxene is very rare as a phenocryst phase in HLP basalts. This cryptic clinopyroxene fractionation may reflect efficient 132

50 LI 45 H [I LI El H 40 Recharge H 0 H Cr) 30 HLilL ?IJJ1IIJ H H H H m LILII 25 rHLI FE 20 L 15 0.4 0.5 0.6 0.7 CaO/AI 203

Figure 4.13. Plot of Sc versus CaO/A1203 of HLP basalts.

removal of all fractionating phases in a crustal magma chamber. This interpretation is supported by the generally low phenocryst content in even fairly evolved basalts.

In this perspective, the common occurrence of <5% olivine and/or plagioclase

phenocrysts across the compositional range of HLP basalts could reflect a small

degree of shallow crystallization, perhaps during ascent. Ti02 enrichment is not

explained by a simple major element model, but could be explained by treating it as

an incompatible trace element as is suggested by the correlation between Ti02 and

K20 and Na20 (Fig. 4.5), and considering the range in Ti02 in primitive HLP

basalts.

To generate major element models for the evolution of HLP basalts we used

MELTS (Ghiorso and Sack, 1995), a computer program that simulates magmatic

processes based on thermodynamically constrained models. Given the scatter in

observed in the major element variation plots (Fig. 4.4), and the lack of a broad 133

spectrum of basalts fromany one volcanic center, we could not seekto model a

specific evolution path. Rather,we sought to create models which fit the bulk of the

data, or defined theextremes in the data. The best fit for the bulkof the data was achieved by models that run at pressures of 1.5-3.0 kb with assimilationbeginning when MgO=8 wt% or earlier.

We began by investigatingthe potential of crystal fractionationalone. A

series of MELTSruns were conducted at pressures of 0.1to 9.9 kb at the fayalite-

magnetite-quartz buffer, with 0.2initial wt% H20. The low H20content reflects

the conclusion of Sisson andLayne (1993) that HAOT eruptedat Medicine Lake

had pre-eruptive H20contents of 0.3 wt%. Modelswere run with different

compositions reflecting therange of primitive HLP basalt compositions, including

an average primitive HLP basalt and compositionsrepresentative of the range in

FeO*, CaO, A1203, andNa20 of primitive HLP basalts (HLP-98-25,HLP-98-47,

92WHLP98, 13 1WHLP98, andan unpublished analysis of A. Grunder, HP-93-33).

The choice of parent compositionhas a notable effect on the first appearance and proportion of olivine (earliercrystallization and higher proportion from high-Fe parent) andclinopyroxene (earlier and more from low-Feparent). The overall trends of the models inmajor element variation diagramswas not vastly different for different HLPparent compositions.

In general, olivine plagioclase, andclinopyroxene began crystallizing within the first 10% of crystallizationat pressures between 1.5 and 3.0 kb. At lower pressures, clinopyroxene appears later in the crystallizingassemblage, and with 134

14 57

55 0 0('J 53 (1 51 10 9 49 8

47 7 45 6

19 4.5

(V) 18 4.0 0 0 .J35 17 z 16 3.0

15 2.5

14 2.0

13 3.0 12 2.5 11 0 2.0 (10 o (.'J 1.5 9

1 .0 8

7 0.5

0.03 3 4 5 6 7 8 9 10 11 4 5 6 7 8 9 10 MgO MgO 3 kb fractional crystallization only 3 kb fractional crystallization alone to 8% MgO then assimilation of low-silica rhyolite at r=1 1 .5 kb fractional crystallization and assimilation r=1 during olivine crystallization, then r=O.33 when plagioclase ± clinopyroxene are crystallizing

Figure 4.14. Results of three MELTS (Ghiorso and Sack, 1995) runs that are consistent with, or bound, most of the data for I-ILP basalts. The starting material in these runs was an average primitive HLP basalt. Varying the source across the range of the most primitive HLP basalts can explain some of the high NaO, high MgO data not intersected by these trends.

plagioclase dominating A1203 depletion is too rapid. At pressures greater than 3.0 kb olivine appears later, or does not appear at all, and with clinopyroxene dominating early crystallization Al203 is elevated. At 1.5-3.0 kb, most data above 135

7-8 wt% MgO can be intersected by model results given variability in parent composition and pressure (Fig. 4.14). Yang and others (1996) demonstrated that

MELTS predicts the onset of clinopyroxene crystallization too early. Given this consideration, the stability conditions for the HLP fractionation assemblage may extend to somewhat greater pressures.

All of the models of pure fractional crystallization (Fig. 4.14) predict constant and declining Si02 until MgO reaches 4.5-5.0 wt%, in clear conflict with

HLP basalt. All models also predict lower K20 than all basalts except those at the base of the envelope in K20-MgO space which follows a pure fractionation trend.

All models predict FeO* enrichment peaking at 15-16 wt% between 4 and 5 wt%

MgO. While some of there are some samples (Fe-Ti basalts) that fall near the high-

FeO segments of these trends, most HLP basalts have 8-12 wt% FeO*. Increases in

5i02 and K20 and steady FeO* require that assimilation accompany fractional crystallization in most, though not all HLP basaltic magmas with MgO contents below -8 wt%. The variation in incompatible trace elements with MgO (Fig. 4.7) also requires assimilation.

Assimilation likely occurred mainly by incorporation of partial melts of country rock. MacLean (1994), Grunder and others (1995), and Johnson and

Grunder (2000) interpret low-silica rhyolites of the HLP to be the product of partial melting of mafic crust, and high-silica rhyolites to be produced by fractionation of low-silica rhyolites. Therefore, low-silica rhyolite is the most reasonable choice for a model assimilant. We used an average low-silica rhyolite, culled from MacLean 136

(1994), Johnson and Grunder (2000), and Grunder unpublished data, as an assimilant. We found good agreement between the bulk of the HLP basalt data and models (Fig. 4.14) in which there is little or no assimilation (r = 0-0.1) at early stages of crystallization (MgO < 8.0 wt%), then higher degrees of assimilation (r =

1) at lower MgO. This assimilation variation is consistent with some time required to heat relatively cold country rock at shallow depths corresponding tol.5-3.0 kb

(5.5-11 km).

Some samples appear to have also undergone the sort of protracted fractionation-recharge history described by Streck and Grunder (1999) for the root zone of the Rattlesnake Tuff magma chamber. This history is reflected by the subordinate trend of increasing Sc with decreasing CaO/A1203 at low CaO/Al203 observed in Figure 4.13. However, this pattern of evolution is relatively uncommon, consistent with the idea that basaltic magmas stalled at depth below rhyolitic magma chambers are unlikely to reach the surface.

Isotopic data are less useful in deducing assimilation/fractional crystallization history than in most magmatic suites. This is because basalts and rhyolites are not clearly distinguished from one another in isotope variation diagrams (Fig. 4.8). Considering spatial variation (Fig. 4.10) reveals more systematic variation with composition. HLP rhyolites have higher 87Sr/86Sr and lower ENd than all Pliocene and Quaternary basalts at the same longitude, but some

HLP rhyolites overlap in 87Sr/86Sr with Miocene basalts. Similarity in 87Sr/86Sr between some rhyolites and basalts may reflect contamination of rhyolites by 137

basalts. All rhyolites for which isotopic data are presented are high silica rhyolites which can have Sr as low as 2 ppm (MacLean, 1994; Streck and Grunder, 1999;

Johnson and Grunder, 2000), making them susceptible to contamination by basalts.

Basalts do not have the same leverage with Nd, so it is not surprising that basalts and rhyolites are more distinct in '43NcI/'44Nd, when spatial variation is seen through. Rhyolites have significant leverage over basalts in the Pb isotopic system

(low-silica rhyolite -10 ppm Pb, average of ten most primitive basalts -1 ppm Pb).

Unfortunately, HLP basalts and rhyolites are indistinguishable in Pb isotopic composition (Fig. 4.8). This could be interpreted as reflecting uniform crustal contamination of basalts, but this is unlikely across the range of fractionation experienced by HLP basalts. A better explanation is that the relatively young

accreted crust from which the rhyolites were derived had not evolved a distinct Pb

isotopic signature. At least one western HLP basaltic andesite (8 1WHILP98)

appears to have interacted with a more evolved assimilant during fractionation,

based on its relatively high 875r/865r (0.70425) and lowENd(+3.2).

SUMMARY PETROLOGIC MODEL FOR GENESIS OF HIGH LAVA PLAINS BASALTIC MAGMAS

Primitive HLP basalts were derived by modest degrees (5-20%) of partial

melting of a mantle source dominated by a depleted (MORB-mantle) component

(>70%), mixed with a primitive mantle (OIB-source) component (<30%), and a

small (<0.2%) Ba-rich subduction component. Some of this melting probably 138

occurred at depths at which garnet was stable (>60 km), but most HLP basaltic magmas appear to have equilibrated near the base of the crust (-37 km). The source of Miocene HLP basalts was isotopically relatively homogeneous. Pliocene and

Quaternary basaltic magmas tapped more diverse sources which were more isotopically evolved than the Miocene sources in the west, and more depleted in the west.

More evolved mafic rocks can be related to primitive melts by fractionation and assimilation at 1.5 to 3 kb (5-11 km). Most basalt compositions lie on a trend suggesting limited assimilation during early fractionation, with increased assimilation below 8 wt% MgO. Some highly evolved basaltic andesites underwent protracted cycles of fractionation and recharge (Streck and Grunder, 1999).

Separation of fractionating phases was generally efficient such that most erupted

HLP lavas are aphanitic or sparsely porphyritic (<5%).

This model for basalt petrogenesis is consistent with the tectonic scenario proposed in chapter 3 and Figure 4.15 in which a plume head emplaced under

western North America (the Yellowstone plume) drove Middle Miocene basaltic

volcanism and conditioned the lithosphere under the High Lava Plains for

subsequent magmatism. This plume head provided heat and some material for HLP

magmatism, consistent with the interpretation of an OIB component in HLP

magmas. The model also describes sublithospheric flow of plume material from

under the thick Precambrian lithosphere of southeastern Idaho toward thin accreted

lithosphere under eastern Oregon. Thermomechanical erosion during westward 139

Figure 4.15. Cartoon depicting the scenario envisioned to explain the distribution of Middle Miocene basaltic vents, and trends of migrating silicic volcanism of the HLP and YSRP. (1) the Yellowstone plume head flattened as it approached the North American lithosphere; (2) magmatism (Columbia River basalt, Steens Basalt, and Northern Nevada Rift; orange lines on map) occured where the plume head was allowed to rise to shallow depths, especially at the edge of the craton where secondaryflowof plume head and perhaps plume material increased activity of the system; the connection between the position of the plume and the site of maximum volcanic eruption would later be marked by the western Snake River Plain (WSRP) graben (see also Fig. 1.5), perhaps reflecting lithospehric weakening due to sublithosphencflowof hot plume material; (3) as the North American plate moved southwest, the plume become established under the continent (no longer connected to the topographic gradient at the craton margin) and left a distinct hotspot trace leading to the Yellowstone Plateau; in the west, crustal volcanism migrated westward because the lag necessary to incubate lithospheric magmatism by conduction and advection increased to the west because less, and cooler, plume head material was emplaced here. Also, sublithospheric plume flow could have drivenflowinto the region under the HLP. 140

/\AH Plume head £ / It 00 k

I LA / 45- 7;fC/j I -\J',' -- /Migrating crustal magmatism A / - / due to conductive and advective A '/ \ heat transfer from plume head occurs only where plume head 40 emplaced under thin extending

_____rnckmL\

130 l2O 110

0 Ma HLP trend develops due to increased VSRP trend develops incubation lime for lrthopherrc magmatism as plate moves over further from center of plume head plume conduit

______C- se-- '- - r1.

Melting occurs in plume head 1 7 Ma only where emplaced under ttiin lithosphere yet near hot center 0 - head has Inle

- diroct eflecl where emplaced - nr under thick lithosphere \Plume

l7Ma I

Figure 4.15 141

sublithospheric flow could explain the presence of an isotopically evolved component in the source of Pliocene and Quaternary basaltic magmas of the eastern

HLP. The petrologic model presented here favors, but does not require, a mantle plume contribution to HLP basaltic magmatism. Given the other links between the

High Lava Plains and Yellowstone-Snake River Plain system, and a viable physical model explaining the relationship, we feel that this is the best current model for magmatism in both provinces.

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CONCLUSIONS

In the preceding chapters I presented the following important observations and first-order interpretations:

-The trend of migration of silicic volcanism across the High Lava Plains

province (HLP), initially defined with K-Ar geochronology, is shown to

be a robust trend utilizing 40Ar/39Ar techniques.

-Basaltic volcanism has been continuous across the HLP since the Miocene

with local hiatuses and several episodes of widespread increased activity

at 7.6, 5.9, and 2-3 Ma. The 7.6 Ma event corresponds with initiation of

High Cascades volcanism and the events may be related to a regional

tectonic event.

-Middle Miocene intermediate to silicic volcanism is widespread in

southeastern Oregon and northwestern Nevada.

-He isotopes are of uniform composition across the HLP with 3He/4He = 9

RA,similar to MORBs with depleted isotopic and trace element

characteristics.

-There is a dichotomy in that HLP basalts have enriched trace element and

isotopic signatures (relative to MORB), but 3He/4He suggestive of an

unusually depleted source. A potential explanation is the broad dispersion 150

of a high-3He/4He source, such as the head of a mantle plume, in the

upper mantle under the HLP.

-HLP basalts are mostly primitive high-alumina olivine tholeiites though

significant variation, including evolved basalts, basaltic andesites, basaltic

trachyandesites, calc-alkaline basalts, and alkali basalts, does occur.

-Major and trace element characteristics reflect varying degrees of

fractional crystallization and assimilation in upper crustal magma

chambers (5-11 km).

-HLP basalts are enriched relative to MORB in incompatible trace elements,

especially Ba, Sr, and Pb.

-HLP basalts also have more evolved isotopic signatures than MORB

-Isotopic characteristics of Pliocene and younger basalts of the HLP and

some trace element ratios (e.g. Zr/Nb) reveal systemic variations across

the HLP with as discontinuity at 119.5 ow.

-Miocene basalts do not show this variation.

-Given the variability of Sr and Nd isotopes, uniform 3He/4He reflects

decoupling from other isotopic tracers.

-Trace element ratios suggest that the primary source of HLP basaltic

magmas is a depleted upper mantle (MORB-like) source, with a varying

contribution of a primitive mantle (OIB-like) source, and a small

contribution from a subducted sediment component. This is consistent 151

with the regional dispersion of plume material postulated to explain

helium isotopic data.

PROBLEMS FOR FUTURE STUDY

The regional model developed in this study could be readily tested by

successful determination of the He isotope composition of Miocene HLP basalts. I

analyzed seven Tertiary basalts for He isotope composition, but all of those

samples had low He concentrations so magmatic 3He/4He ratios could not be

determined. Further attempts to get meaningful 3He/4He ratios from Tertiary basalts may be warranted. It may also be productive to extend helium isotope

studies into the northwestern Basin and Range province immediately south of the

High Lava Plains.

Other potential lines of future research include: 40Ar/39Ar dating of rhyolites of the western HLP to create a precise and accurate database for all rhyolites of the HLP; integrating the geochronologic database of HLP volcanic rocks with a structural database to document the temporal evolution of faulting in the HLP; detailed study of the few young basaltic lava fields north of the HLP

(Walker and MacLeod, 1991); and detailed studies of demonstrably comagmatic

suites of HLP basalts to better resolve the processes of genesis and evolution of

HLP basaltic magmas. 152

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APPENDIX 1: NEW MAJOR AND TRACE ELEMENT ANALYSES OF HIGH LAVA PLAINS BASALTS

XRF and ICP-MS data for all samples analyzed in this study. Methodsare described in chapter 4. Percent relative error for ICP-MS analysesare given in table 4.1. 166

Sample 1WHLP98 1WHLP99 2WHLP97 2WHLP98 3WHLP97 3WHLP98 3WHLP99b4WHLP98 Lat. 43.9399 43.9058 43.9220 43.9227 43.9228 43.9229 43.9251 43.9231 Lone. 121.0054 121.0060 121.0048 121.0048 121.0048 121.0048 121.0743 121.0045 Major Elements XAF (Weight %) Si02 49.63 54.94 53.91 53.40 52.26 52.99 52.81 52.28 Ti02 1.82 1.12 1.24 1.28 1.38 1.28 1.11 1.39 A1203 16.57 18.66 17.04 17.25 17.17 17.29 17.69 17.21 FeO 9.77 7.10 9.16 9.08 9.86 9.36 7.94 9.84 MrO 0.17 0.13 0.17 0.17 0.17 0.17 0.15 0.18 MgO 6.53 4.47 4.84 5.19 5.38 4.95 6.87 5.20 C 10.63 8.25 7.61 7.89 8.23 8.03 8.86 8.31 Na20 3.09 3.83 3.82 3.75 3.56 3.92 3.36 3.61 K20 1.28 1.21 1.51 1.32 1.37 1.33 0.85 1.35 P205 0.50 0.30 0.69 0.67 0.62 0.68 0.36 0.63

Mg# 62.0 60.6 56.3 58.2 57.1 56.4 67.9 56.3 Trace-Elements XRF (ppm) 34 22 28 24 22 22 23 29 V 268 174 177 181 206 189 191 206 Cr 110 48 75 83 97 80 167 96 Ni 51 33 47 60 69 63 125 67 Qi 33 66 43 52 40 39 74 46 Zn 87 74 96 94 92 92 74 96 19 20 21 18 18 15 17 20 23 14 15 13 13 12 11 14 Sr 744 788 536 503 482 513 510 483 V 29 19 26 28 28 30 22 30 Zr 175 103 169 160 151 160 115 146 Nb 10 6.5 12.2 12.9 11.9 12.2 8.5 10.5 Ba 912 403 637 604 567 621 345 563 La 19 17 11 21 8 17 14 18 Ce 55 20 59 53 53 57 36 64 Pb 6 3 1 1 7 7 3 3 Th 3 3 2 0 4 0 1 0 Trace-Elements ICP-MS (ppm) Sc 19 24 22 26 25 V 190 230 Cr 47 91 91 104 111 Co 34 36 40 44 51 Ni 37 62 66 74 80 Cu 65 55 51 51 51 Zn 73 99 93 96 102 14.5 15.6 13.8 13.8 14.3 Sr 781 552 533 499 519 Y 18.1 31.2 29.5 30.3 33.5 Zr 100 179 165 155 163 Nb 7.3 13.6 13.0 12.0 12.4 Sn 0.94 1.24 1.21 1.19 1.23 Ce 0.5 0.3 0.2 0.3 0.3 Ba 400 667 627 592 621 La 12.5 25.6 23.8 21.7 22.5 Ce 28.5 57.5 52.6 48.2 50.4 Pr 4.0 7.6 7.1 6.4 8.8 Nd 17.4 31.8 29.7 28.1 29.4 Sm 3.6 6.6 6.0 5.8 6.3 E.i 1.26 1.84 1.82 1.80 1.93 3.9 6.0 5.8 5.7 6.1 Tb 0.58 0.90 0.88 0.87 0.93 Dy 3.2 5.2 5.1 5.2 5.4 Ho 0.59 1.02 0.97 1.01 1.07 Er 1.73 2.84 2.70 2.91 2.97 Tm 0.27 0.47 0.41 0.43 0.50 Yb 1.6 2.7 2.6 2.7 3.0 Lu 0.26 0.42 0.41 0.41 0.46 Hf 2.33 3.91 3.81 3.57 3.74 Ta 0.49 0.72 1.22 1.50 1.33 Pb 3.7 6.5 5.5 5.2 5.8 Th 1.32 1.13 0.99 0.99 1.07 U 0.51 0.48 0.41 0.44 0.44 167

Sample 5WHLP97 6WHLP98 8WHLP97 IOWHLP9813W1-ILP9S14WHLP97I4WHLP9BI5WHLP9B Lat. 439228 43.9229 43.9281 43.6465 43.0913 43.9180 43.0913 43.0913 Long. 121.0033 121.0033 121.0051 120.8477 120.8384 120.8381 120.8381 120.8375 Major Elements XRF (Weight %) S102 51.66 56.32 49.37 48.83 48.27 51.18 49.35 48.85 Ti02 1.24 2.10 1.63 1.19 1.56 1.13 1.62 1.51 Al203 17.86 14.89 15.81 17.35 16.96 18.03 17.19 17.59 FaQ 9.06 9.76 9.22 8.97 11.65 9.10 11.59 11.35 MrO 0.15 0.19 0.16 0.16 0.18 0.17 0.18 0.18 MgO 6.15 3.43 8.22 9.03 8.15 6.48 6.72 6.65 9.38 7.19 10.60 11.06 9.18 9.56 8.72 9.25 Na20 3.45 3.94 2.67 3.02 3.24 3.37 3.57 3.67 K20 0.71 1.28 1.72 0.19 0.45 0.77 0.68 0.58 P205 0.34 0.90 0.60 0.19 0.34 0.22 0.39 0.36

Mg# 62.4 46.2 68.5 71.1 63.1 63.5 58.6 58.9 Trace-Elements XRF (ppm) 29 39 33 30 27 30 30 22 V 210 210 257 197 274 237 275 260 Cr 98 33 332 269 136 107 76 82 Ni 78 12 126 137 126 92 83 94 Cu 33 35 35 52 91 85 107 95 Zn 84 103 81 68 97 80 99 95 19 17 19 15 19 20 18 19 10 25 27 1 3 11 6 3 Sr 569 337 1199 215 352 509 465 504 V 24 50 27 28 29 22 28 27 Zr 116 152 195 106 93 90 110 100 Nb 6.8 9.3 7.1 6.3 5.1 3.7 6.8 6.1 Ba 380 574 1449 98 243 316 332 339 L.a 0 13 29 5 0 4 7 14 Ce 26 39 66 28 14 8 32 13 Pb 1 6 9 3 1 0 1 0 Th 0 4 3 0 1 0 0 0 Trace-Elements IGP-MS (ppm) Sc 26 32 33 41 32 29 V 246 271 263 Cr 106 30 323 307 147 82 Co 42 29 70 51 49 95 Ni 88 19 128 139 125 104 Cu 45 36 52 58 89 99 Zn 91 107 83 72 91 99 F 8.6 27.9 28.0 1.5 3.4 4.3 Sr 613 356 1183 231 350 502 V 27.1 56.2 28.8 29.6 29.7 26.6 Zr 116 166 170 114 96 102 Nb 8.8 10.5 8.6 6.0 5.8 7.3 Sn 1.12 1.50 1.23 1.04 0.79 1.31 Ce 0.3 1.1 0.4 0.0 0.2 0.2 Ba 432 634 1435 124 258 341 La 14.9 20.6 28.6 6.4 8.8 10.9 Ce 32.4 47.3 71.3 16.9 23.7 27.2 Pr 4.9 6.8 10.5 2.6 3.4 3.8 Nd 22.5 32.7 45.2 12.5 16.1 17.6 Sm 5.1 8.3 8.2 3.6 4.2 4.4 1.61 2.57 2.49 1.27 1.47 1.49 4.6 8.2 6.9 4.0 4.5 4.5 Tb 0.77 1.36 0.94 0.73 0.77 0.72 Dy 4.4 8.0 5.1 4.5 4.8 4.4 Ho 0.87 1.76 0.96 1.03 1.03 0.90 Er 2.51 4.88 2.68 2.89 2.80 2.41 Tm 0.40 0.78 0.41 0.49 0.47 0.42 Yb 2.4 4.5 2.3 3.0 2.6 2.4 Lu 0.40 0.70 0.36 0.45 0.40 0.38 Hf 2.57 4.17 4.93 2.63 2.41 2.44 Ta 0.47 0.73 0.99 0.80 0.28 1.71 Pb 3.6 6.1 10.6 1.5 2.5 3.3 Th 0.84 2.93 2.11 0.31 0.29 0.52 1) 0.39 1.07 0.90 0.16 0.11 0.21 168

Sample 1 7WHLP981 9WHLP9820WHLP9821 WHLP9722WHLP9824WHLP9825WHLP9829WHLP98 Lat. 43.0913 43.0909 43.0907 43.7488 43.0907 43.0907 43.3338 43.5909 Long. 120.8369 120.8366 120.8363 120.9682 120.8357 120.8381 120.6711 121.1498 Major ElementsXRF(Weight %) Si02 48.76 48.60 48.31 49.16 48.65 48.82 51.53 52.10 Ti02 1.44 1.44 1.43 1.26 1.44 1.08 1.08 0.91 Al203 16.52 16.55 16.58 17.25 16.97 16.93 17.07 16.98 FeO 11.33 11.69 11.67 9.41 11.45 10.45 8.29 7.67 MrO 0.19 0.19 0.19 0.17 0.19 0.18 0.15 0.13 MgO 7.72 7.53 7.68 8.74 6.93 7.54 8.00 9.61 CD 9.82 9.93 10.00 10.10 10.53 11.45 9.91 8.57 Na20 3.22 3.13 3.21 3.05 3.06 2.86 3.06 3.23 K20 0.67 0.59 0.59 0.52 0.49 0.47 0.66 0.62 P205 0.34 0.32 0.33 0.34 0.28 0.22 0.23 0.17

Mg# 62.5 61.1 61.6 69.4 59.6 63.8 70.2 75.3 Trace-ElementsXRF(ppm) 34 29 28 30 40 32 31 24 V 266 274 253 199 261 256 187 181 Cr 230 206 210 255 149 161 237 520 Ni 121 127 127 157 95 92 113 322 102 99 99 64 106 117 54 68 Zn 92 90 87 69 88 72 69 62 17 17 17 15 22 17 18 18 9 6 7 8 6 6 12 11 Sr 496 465 468 332 409 472 394 476 V 27 29 29 24 29 24 20 15 Zr 107 98 95 111 85 65 101 91 Nb 4.135 5.5 5.1 11 4.1 2.1 6.739 5.616 Ba 399 358 370 168 311 342 232 233 La 0 5 7 12 2 12 12 0 Ce 39 23 29 27 25 14 25 13 Pb 0 2 0 0 1 0 2 1 Th 0 0 2 4 0 0 3 0 Trace-Elements ICP-MS (ppm) 29 35 30 22 V 189 249 195 Cr 272 166 243 362 Co 52 50 52 51 Ni 151 91 120 284 Cu 68 111 58 74 Zn 72 72 70 64 8.0 6.6 12.0 9.7 Sr 334 470 374 503 V 25.9 22.9 22.8 16.9 Zr iio 64 97 87 Nb 11.4 3.6 8.0 6.6 Sn 0.94 0.53 0.74 1.10 Ge 0.2 0.1 0.4 0.3 Ba 185 348 251 252 La 10.2 7.5 9.8 8.4 Ce 25.3 21.0 23.8 19.8 P1 3.4 3.1 3.2 2.7 Nd 15.1 14.2 13.8 11.3 Sm 3.7 3.4 3.2 2.9 1.24 1.23 1.11 0.98 3.9 3.8 3.6 2.9 Tb 0.67 0.62 0.59 0.50 Dy 4.1 3.8 3.8 2.8 Ho 0.88 0.85 0.78 0.58 Er 2.42 2.26 2.13 1.64 Tm 0.41 0.39 0.37 0.28 Yb 2.5 2.2 2.2 1.6 Lu 0.36 0.35 0.36 0.25 Hf 2.41 1.87 2.32 2.03 Ta 0.78 0.23 1.11 1.58 Pb 2.3 2.7 3.3 3.4 Th 0.94 0.56 1.34 0.77 U 0.37 0.30 0.45 0.43 Sample 30WHLP9835WHLP98 37BJ95 4OWHLP9843WHLP9848WHLP985OWHLP9853WHLP98 Lat. 43.5535 43.5228 43.5500 43.5767 43.7241 43.7925 43.5947 43.6036 Lone. 121.2917 120.8642 120.8800 120.9204 120.9978 120.8550 120.7321 120.7854 Major ElementsXRF(Weight %) Si02 53.49 49.34 51.77 51.04 49.98 55.05 48.19 56.07 Ti02 1.09 1.47 1.16 1.20 0.91 1.28 1.63 2.10 A1203 17.59 16.75 18.04 18.34 18.32 17.39 16.72 15.77 FeO 7.61 9.11 8.53 8.62 7.09 8.53 10.76 10.05 MrO 0.14 0.17 0.15 0.15 0.13 0.15 0.18 0.19 MgO 6.02 9.20 6.42 6.61 8.18 3.90 8.26 3.04 C 9.26 9.93 9.37 9.55 11.31 7.45 10.35 6.53 Na20 3.68 3.10 3.53 3.59 2.93 3.98 3.27 4.69 K20 0.89 0.56 0.77 0.62 0.83 1.69 0.35 1.17 P205 0.24 0.37 0.26 0.27 0.31 0.58 0.28 0.40

65.9 71.2 64.8 65.2 73.8 52.8 65.2 42.5 Trace-ElementsXRF(ppm) 28 31 30 29 23 22 28 33 V 188 207 209 217 175 199 234 232 Cr 134 336 68 75 172 52 224 8 Ni 61 174 91 91 122 16 132 0 0,j 61 66 60 54 83 40 60 12 Zn 66 80 76 75 61 95 81 98 23 18 18 19 16 22 19 22 Pb 16 8 12 4 11 17 4 25 Sr 410 311 532 528 911 569 273 408 Y 26 30 21 23 17 27 31 35 Zr 127 123 113 106 106 175 119 129 Nb 6.954 12 6.4 7.4 6.1 11.674 7.2 7.1 Ba 282 190 285 272 505 729 102 407 La 15 14 9 14 33 14 8 1 Ce 35 26 38 34 45 57 21 30 Pb 3 0 3 0 2 7 0 6 Th 3 4 2 1 2 2 0 4 Trace-Elements ICP-MS (ppm) Sc 27 28 26 22 35 35 V 176 193 241 Cr 149 304 196 55 241 8 Co 41 56 49 41 55 27 Ni 67 155 127 26 135 8 Co 65 65 88 51 63 17 Zn 70 76 66 98 96 109 Pb 16.1 9.3 11.7 19.4 4.1 26.4 Sr 416 313 938 578 275 434 V 27.1 29.0 17.4 30.6 33.8 37.4 Zr 127 127 108 186 126 140 Nb 8.1 12.4 7.3 13.0 8.6 8.4 Sn 1.47 1.15 0.59 1.38 1.07 1.41 Ce 0.6 0.2 0.3 0.4 0.0 1.1 Ba 302 187 527 794 142 461 La 12.1 10.8 21.6 25.1 8.6 15.0 Ce 28.5 26.5 49.2 56.9 22.3 33.9 3.9 3.7 6.6 7.3 3.3 5.1 Nd 17.0 17.1 27.6 30.0 15.7 23.0 Sm 4.1 4.1 4.8 6.2 4.4 5.9 1.25 1.39 1.52 1.86 1.55 1.94 4.3 4.6 4.4 6.0 4.9 6.0 Tb 0.71 0.77 0.60 0.88 0.86 0.99 Dy 4.5 4.8 3.1 5.2 5.4 6.0 Ho 0.92 0.99 0.59 1.04 1.15 1.32 Er 2.52 2.77 1.65 2.83 3.16 3.39 Tm 0.41 0.45 0.30 0.45 0.53 0.54 Yb 2.5 2.7 1.5 2.8 3.1 3.4 Lu 0.37 0.44 0.24 0.45 0.46 0.47 Hf 3.26 3.01 2.71 4.10 3.01 3.68 Ta 1.35 1.88 0.80 1.67 0.59 0.92 Pb 3.6 2.4 4.2 7.7 1.8 5.8 Th 1.67 1.02 2.40 1.70 0.53 2.43 U 0.64 0.47 0.76 0.63 0.23 0.97 170

Sample 55WHLP986OWHLP9869WHLP987OWHLP9871 WHLP9874WHLP9875WHLP9876WHLP98 Lat. 43.5324 43.6897 43.8989 43.8987 43.9266 43.9575 43.8325 43.7221 Long. 120.8245 120.8762 120.8339 120.8327 120.8141 120.8396 120.5635 120.7536 Major Elements XRF (Weight %) S102 52.01 52.86 53.12 52.06 52.61 55.50 48.60 52.15 Ti02 1.74 1.34 1.42 1.03 1.47 1.18 1.61 1.17 A1203 16.56 16.89 17.47 19.47 17.45 17.03 16.60 17.41 FeO 11.33 7.88 8.85 7.60 9.37 8.19 11.11 7.95 MrO 0.19 0.15 0.18 0.14 0.18 0.16 0.19 0.14 MgO 4.88 6.70 4.70 5.11 4.42 4.33 7.67 7.02 8.24 9.72 8.23 10.21 8.12 7.24 10.56 9.81 Na20 3.96 3.41 3.79 3.49 4.02 3.86 3.09 3.44 K20 0.79 0.74 1.47 0.68 1.55 1.91 0.31 0.64 P205 0.31 0.30 0.76 0.23 0.81 0.59 0.27 0.26

Mg# 51.2 67.5 56.5 62.1 53.5 56.3 62.8 68.3 Trace-Elements XRF (ppm) 33 26 27 22 23 17 31 30 V 286 210 220 205 197 175 271 204 Cr 23 195 72 65 74 62 233 209 Ni 25 72 40 32 34 41 114 77 Co 32 82 53 36 56 69 63 58 Zn 110 72 100 68 99 93 85 66 20 16 18 20 17 20 19 15 9 9 10 10 14 20 2 9 Sr 393 478 540 616 543 509 294 478 Y 33 27 33 19 33 28 29 23 Zr 129 130 165 69 171 164 97 123 Nb 7.2 8 12.4 4.8 13 10.8 5.4 6.579 Ba 366 285 708 360 703 749 204 236 La 11 3 21 0 22 34 0 2 Ce 35 18 66 24 55 38 29 35 Pb 0 1 4 3 5 6 0 2 Th 0 2 0 0 0 2 0 3 Trace-Elements ICP-MS (ppm) Sc 26 20 V 219 176 Cr 83 67 Co 37 32 Ni 44 47 Co 63 74 Zfl 104 91 14.2 20.2 Sr 555 509 Y 36.4 29.9 Zr 180 171 Nb 13.6 12.2 Sn 1.23 1.20 Ce 0.3 0.3 Ba 715 757 La 26.4 24.5 Ce 58.8 53.3 7.8 6.9 Nd 33.6 28.7 Sm 7.0 5.8 1.97 1.72 Gd 6.5 5.6 Tb 0.96 0.87 Dy 5.8 4.9 Ho 1.14 0.97 Er 3.23 2.74 Tm 0.56 0.47 Yb 3.1 2.6 Lu 0.45 0.41 Hf 3.96 3.92 Ta 0.95 0.70 Pb 6.8 7.3 lii 1.00 1.41 U 0.43 0.57 171

Sample 77WHLP9878WHLP9881WHLP9882WHLP9885WHLP9886WHLP9889WHLP9892WHLP98 Lat. 43.6783 43.7187 43.6133 43.5654 43.3458 43.4259 43.4570 43.5211 Long. 120.7409 120.6519 120.6870 120.6819 120.6804 120.7025 120.8220 120.7803 Major ElementsXRF(Weight %) Si02 54.61 49.39 54.03 52.36 51.02 51.20 55.08 48.26 Ti02 1.95 1.26 1.71 1.62 1.62 1.55 1.11 1.04 A1203 15.91 17.50 16.27 16.55 17.22 17.21 16.25 17.61 FeO 11.24 9.38 10.57 10.73 8.78 8.67 7.36 9.26 MrO 0.20 0.17 0.18 0.19 0.16 0.15 0.14 0.18 MgO 3.32 8.09 4.26 5.29 6.82 6.97 7.38 9.21 C 6.83 10.56 7.78 8.40 9.38 9.36 7.92 11.57 Na20 4.21 3.13 3.83 3.65 3.69 3.61 3.24 2.67 K20 1.35 0.32 1.08 0.93 0.95 0.91 1.33 0.09 P205 0.39 0.21 0.30 0.29 0.38 0.36 0.19 0.12

Mg# 41.9 67.8 49.6 54.6 65.5 66.2 71.0 70.8 Trace-ElementsXRF(ppm) 32 34 27 37 24 22 22 40 V 243 214 281 256 213 199 162 230 Cr 13 223 20 39 176 188 271 225 Ni 1 143 8 38 91 100 152 146 Co 19 92 25 43 58 62 49 78 Zn 124 70 106 102 70 69 62 61 22 18 22 21 17 18 18 16 23 3 17 13 13 13 26 1 Sr 362 296 402 384 427 414 289 181 Y 40 27 34 31 27 28 27 24 Zr 169 81 129 119 165 156 113 59 Nb 10.3 6.1 7.7 7.6 16.669 16.4 5.6 2.5 Ba 546 153 438 372 268 285 352 64 La 17 8 14 18 19 6 6 5 Ce 25 39 31 35 51 21 22 13 Pb 6 0 2 3 1 1 5 0

Th 1 1 1 4 2 2 3 0 Trace-Elements ICP-MS (ppm) Sc 34 27 30 40 V 201 215 Cr 261 16 186 225 Co 53 37 54 54 Ni 144 16 98 147 Cu 100 25 68 80 Zn 77 109 81 65 3.5 18.9 13.4 0.5 Sr 322 414 430 180 Y 27.6 34.5 30.3 22.7 Zr 84 137 174 60 Nb 5.6 8.7 18.0 2.7 Sn 0.87 1.33 1.51 0.38 Ce 0.0 0.6 0.3 0.0 Ba 184 479 300 63 La 6.6 13.5 15.6 2.7 Ce 16.5 31.6 37.0 8.0 Pt 2.5 45 4.9 1.3 Nd 12.2 20.5 21.3 6.7 Sm 3.3 5.0 4.9 2.2 1.21 1.65 1.66 0.98 3.7 5.4 5.1 2.9 Tb 0.70 0.92 0.83 0.56 Dy 4.3 5.5 5.1 3.6 Ho 0.94 1.12 0.99 0.80 2.55 3.15 2.78 2.22 Tm 0.44 0.48 0.46 0.41 Yb 2.5 3.1 2.7 2.3 Lu 0.37 0.47 0.40 0.36 Hf 2.04 3.46 3.84 1.47 Ta 0.66 0.59 2.52 0.18 Pb 1.3 5.1 3.3 0.9 Th 0.38 1.88 1.59 0.09 U 0.18 0.72 0.57 0.05 172

Sample 1 02WHLP98 1 O3WHLP98 1 O5WHLP98 1 06WHLP98 1 09WHLP98 11 8WHLP98 1 23WHLP98 1 24WHLP98 Lat. 43.1160 43.1157 43.1140 43.1151 43.0956 43.4395 43.7284 43.7617 Long. 120.9513 120.9492 120.9430 120.9441 120.8027 120.2697 120.4059 120.4344 Major ElementsXRF(Weight %) Si02 48.79 48.34 49.70 49.57 49.11 54.88 48.97 48.95 Ti02 1.43 1,43 1.30 1.26 1.53 1.58 1.02 1.47 Al203 16.68 16.87 17.14 17.32 17.07 15.73 17.83 17.10 FeO 10.52 10.54 10.08 10.56 10.42 9.11 8.88 9.61 Mr 0.19 0.19 0.18 0.18 0.19 0.17 0.16 0.17 M3 8.69 8.84 8.13 7.44 8.02 5.20 8.79 8.71 CeO 10.22 10.18 9.43 9.72 9.76 8.35 10.90 10.06 Na20 2.89 3.02 3.27 3.31 3.16 3.62 2.96 3.30 K20 0.34 0.34 0.48 0.41 0.41 1.06 0.27 0.38 P205 0.25 0.26 0.29 0.23 0.32 0.29 0.21 0.25

Mg# 66.8 67.2 66.3 63.2 65.2 58.2 70.7 68.9 Trace-ElementsXRF(ppm) 34 33 32 30 29 25 29 33 V 250 239 238 230 270 252 211 204 Cr 242 246 189 177 187 105 234 245 Ni 162 160 144 132 137 51 171 155 Co 85 91 79 92 101 65 87 60 Zn 88 87 88 88 93 87 66 74 17 17 18 19 21 19 14 17 Pb 4 3 4 4 2 16 1 3 Sr 325 323 424 390 387 249 327 263 V 29 29 25 25 28 41 21 30 Zr 87 89 78 73 86 143 81 109 Nb 4.7 5.2 3.3 4.8 3.7 6.9 3.748 6.9 191 172 224 221 287 441 138 135 La 0 8 13 1 15 3 0 9 Ce 17 17 24 9 34 46 25 23 Pb 0 1 1 0 0 2 0 0 Th 2 0 0 1 0 2 3 2 Trace-Elements ICP-MS (ppm) Sc 32 33 30 32 30 V 245 245 208 Cr 251 240 194 105 231 Co 58 51 64 37 59 Ni 159 151 144 57 176 Cu 91 91 101 71 90 Zn 88 91 92 90 69 Pb 3.4 4.3 5.4 16.7 2.2 Sr 325 353 396 257 322 V 30.0 31.1 26.3 43.4 20.9 Zr 91 99 77 155 78 Nb 5.6 6.0 4.5 8.5 5.7 Sn 0.84 1.05 0.72 1.63 0.60 cs 0.1 0.1 0.2 0.4 0.1 Se 199 205 220 451 158 La 7.4 7.7 6.6 13.3 6.1 Ce 19.5 20.3 17.3 31.2 15.7 2.9 3.1 2.6 4.6 2.2 Nd 13.9 14.7 12.5 20.9 10.1 Sm 3.9 4.0 3.5 5.4 2.7 Si 1.36 1.39 1.24 1.63 1.07 4.3 4.2 3.9 5.8 3.2 Tb 0.74 0.79 0.69 1.03 0.56 Dy 4.7 4.7 4.2 6.5 3.4 Ho 1.01 1.00 0.91 1.44 0.70 Er 2.83 2.91 2.44 4.06 1.96 Tm 0.49 0.47 0.40 0.67 0.32 Yb 2.8 2.8 2.4 4.1 2.0 Lu 0.41 0.44 0.37 0.61 0.31 Hf 2.29 2.51 2.05 4.20 1.79 Ta 0.70 0.43 0.39 0.54 1.33 Pb 2.0 2.6 2.8 4.1 1.8 Th 0.36 0.35 0.58 2.08 0.30 U 0.18 0.19 0.24 0.79 0.14 173

Sample 125WHLP98 128WHLP98 13OWHLP98 131WHLP98 132WHLP98 133WHLP98138CHLP98 141 WHLP98 Lat. 43.7851 43.81 74 43.6538 43.6547 43.9092 43.8912 43.4659 43.5402 Long. 120.4282 120.4790 120.1027 120.1002 119.9406 119.5334 119.8200 119.7814 Major ElementsXRF(Weight %) Si02 49.32 48.51 48.53 49.06 48.75 50.47 48.78 49.92 1102 1.16 1.70 1.64 0.90 1.31 1.14 0.68 1.27 A1203 17.40 16.53 17.18 17.58 17.02 18.47 18.38 17.40 FeO 9.14 8.90 10.43 8.12 9.76 9.28 7.62 9.07 MrO 0.16 0.16 0.19 0.16 0.19 0.18 0.15 0.17 MgO 9.05 8.31 7.54 9.47 8.23 5.97 9.47 7.85 CD 10.20 11.21 10.69 11.95 11.47 10.75 12.20 10.46 Na20 3.07 2.61 3.08 2.44 2.60 3.06 2.44 3.09 K20 0.28 1.52 0.40 0.16 0.37 0.45 0.17 0.45 P205 0.21 0.55 0.33 0.15 0.31 0.24 0.10 0.32

Mg# 70.7 69.5 63.8 74.0 67.3 61.1 75.2 67.9 Trace-ElementsXRF(ppm) 27 31 33 34 42 29 35 29 V 204 251 243 204 265 233 171 235 Cr 268 262 190 310 215 243 184 175 Ni 181 98 113 188 116 163 157 116 103 66 75 79 76 74 86 75 Zn 72 75 78 58 72 86 48 79 19 17 18 16 16 16 14 15 2 50 2 1 3 3 0 6 Sr 326 965 262 203 243 375 176 397 V 22 25 34 24 27 23 20 25 Zr 72 203 128 60 77 78 49 77 Nb 5 13.7 9.6 3.3 7.1 6.7 5.5 5.4 Ba 206 1185 214 144 270 248 76 243 La 9 16 6 15 7 12 4 15 Ce 18 55 19 16 23 25 8 16 Pb 0 6 0 0 0 0 0 0 Th 1 2 0 0 1 1 1 3 Trace-Elements ICP-MS (ppm) Sc 27 35 35 37 37 31 V 265 251 221 Cr 301 294 212 319 212 211 Co 53 47 55 58 63 46 NI 169 113 117 197 154 119 Co 103 73 74 83 89 81 Zn 75 83 83 61 49 85 2.8 53.7 3.1 1.5 1.5 4.6 Sr 348 1000 263 206 184 450 V 22.8 27.8 34.3 24.1 19.2 27.8 Zr 81 222 133 62 53 88 Nb 5.6 16.3 8.7 3.7 4.5 5.6 Sn 0.89 1.72 1.07 0.27 0.66 0.91 Ce 0.1 0.5 0.1 0.0 80 0.1 Ba 210 1265 213 145 74 281 La 6.3 29.5 9.2 4.9 3.1 8.9 Ce 16.3 70.6 23.1 11.8 8.9 21.7 Pr 2.4 10.4 3.4 1.8 1.2 3.2 Nd 11.4 44.9 16.7 8.4 5.0 15.0 Sm 3.1 8.3 4.4 2.5 1.5 3.7 1.15 2.47 1.58 0.94 0.64 1.31 3.4 7.0 5.0 3.0 2.1 3.9 Tb 0.59 0.95 0.86 0.56 0.42 0.70 Dy 3.8 5.0 5.3 3.6 2.9 4.5 Ho 0.82 0.99 1.16 0.77 0.69 0.91 Er 2.24 2.68 3.21 2.32 1.98 2.62 Tm 0.38 0.43 0.58 0.39 0.35 0.41 Yb 2.2 2.2 3.0 2.3 2.3 2.5 Lu 0.34 0.34 0.45 0.37 0.34 0.35 Hf 1.86 5.84 3.07 1.55 1.14 2.19 Ta 0.83 1.07 0.58 0.43 1.67 0.34 Pb 1.8 7.0 1.7 1.1 0.7 2.2 Th 0.38 2.84 0.61 0.29 0.23 0.33 U 0.16 1.29 0.18 0.12 0.07 174

Sample 145CHLP98 147CHLP98 148CHLP98 149WHLP98 15OCHLP98 151CHLP98 152CHLP98 154CHLP98 Lat. 43.4685 43.2468 43.2466 43.2466 43.2466 43.2463 43.2463 43.3117 Loncj. 119.5532 119.5299 119.5299 119.5302 119.5308 119.5311 119.5314 119.5341 Major Elements XRF (Weight %) S102 50.75 48.97 48.86 48.27 48.90 49.27 49.30 48.98 Ti02 1.65 1.49 1.41 1.93 1.36 1.47 1.49 1.62 A1203 16.81 17.19 16.75 16.53 17.10 16.95 16.94 17.08 FeO 9.64 9.83 10.34 11.46 9.81 9.72 9.60 10.12 MriO 0.19 0.19 0.18 0.21 0.19 0.18 0.19 0.19 MgO 7.12 7.97 8.57 7.60 8.39 8.23 8.32 7.76 C 9.45 10.43 9.98 9.63 10.45 10.35 10.29 10.66 Na20 3.28 3.05 3.02 3.14 2.89 2.95 2.98 3.00 K20 0.84 0.56 0.58 0.66 0.56 0.55 0.56 0.31 P205 0.27 0.32 0.31 0.59 0.34 0.32 0.32 0.30

Mp# 64.3 66.4 66.9 61.8 67.6 67.4 67.9 65.2 Trace-Elements XRF (ppm) 34 34 32 34 30 30 33 39 V 252 267 257 287 218 254 260 254 Cr 93 217 233 165 177 222 220 187 Ni 71 157 155 123 144 151 160 122 52 104 95 78 101 112 112 69 Zn 82 82 79 96 85 79 80 83 19 18 20 18 14 17 16 19 20 7 6 6 4 6 6 2 Sr 240 316 320 362 293 313 311 273 V 35 27 25 34 29 28 27 30 Zr 129 92 93 136 102 91 92 106 Nb 10.6 6.3 6.002 9 6.2 4.9 5.8 5.3 Ba 208 318 302 459 347 362 337 188 La 0 6 6 24 5 18 6 2 Ce 36 35 22 36 34 24 41 31 Pb 1 1 0 1 0 0 1 1 Th 3 0 3 1 2 0 0 0 Trace-Elements ICP-MS (ppm) Sc 34 31 33 33 34 V 255 246 248 Cr 100 242 179 235 191 Co 52 73 48 49 51 Ni 81 157 124 151 121 01 61 102 84 108 71 Zn 87 84 100 83 85 22.4 6.8 7.2 7.8 3.9 Sr 254 329 387 332 278 V 38.3 27.1 35.7 28.5 31.4 Zr 141 93 145 83 109 Nb 11.7 7.1 9.2 6.8 6.4 Sn 1.73 0.84 1.07 0.95 0.89 Ge 1.0 0.0 0.1 0.0 0.1 Ba 232 328 489 353 176 La 10.3 8.7 14.0 8.9 7.2 Ce 25.6 22.0 337 22.4 19.4 Pr 3.5 3.1 4.9 3.2 2.9 Nd 16.5 14.4 22.8 15.2 13.9 Sm 4.5 3.8 5.7 4.0 4.1 1.50 1.40 1.97 1.47 1.37 5.1 4.0 5.5 4.2 4.5 Tb 0.90 0.72 0.96 0.73 0.79 Dy 5.8 4.5 5.7 4.5 5.0 Ho 1.21 0.94 1.22 0.96 1.06 Er 3.56 2.60 3.32 2.75 3.03 Tm 0.60 0.45 0.51 0.45 0.47 Yb 3.7 2.5 3.2 2.5 2.9 Lu 0.57 0.36 0.48 0.37 0.45 Hf 3.34 2,24 3.23 2.18 2.62 Ta 1.18 1.63 0.79 0.70 0.37 Pb 4.2 2.3 2.7 2.0 1.8 Th 1.97 0.63 0.56 0.44 0.43 U 1.09 0.15 0.29 0.25 0.20 175

Sample 156WHLP98HLP98O1 HLP9802 HLP9803 HLP9805 HLP9807 HLP9809 HLP9812 Lat. 43.3119 43.2182 43.2173 43.2167 43.2198 43.1264 43.1263 43.1261 Long. 119.5338 120.5252 120.5257 120.5333 120.5417 120.3908 120.3900 120.3898 Major Elements XRF (Weight %) S102 48.82 54.84 55.01 55.72 56.61 54.19 55.16 52.15 Ti02 1.60 1.08 1.09 1.06 1.13 1.83 2.04 1.23 A1203 17.22 16.90 16.93 16.71 16.61 15.53 15.45 17.49 FeO 10.40 8.04 7.80 7.79 7.86 10.41 9.58 8.98 MnO 0.19 0.14 0.15 0.14 0.15 0.19 0.21 0.17 MgO 7.54 5.55 5.51 5.21 4.42 3.91 3.73 6.35 C 10.58 8.43 8.43 8.07 7.63 7.80 7.52 8.83 Na20 3.04 3.42 3.32 3.38 3.76 4.31 4.23 3.40 K20 0.31 1.33 1.50 1.65 1.54 1.25 1.33 1.04 P205 0.30 0.27 0.27 0.27 0.28 0.57 0.75 0.36

Mg# 63.9 62.7 63.3 62.0 57.8 47.8 48.7 63.3 Trace-Elements XRF (ppm) 37 24 25 24 21 29 32 25 V 256 207 188 199 201 297 274 219 Cr 177 100 100 98 83 19 16 127 Ni 119 71 70 70 43 5 5 90 Cu 81 80 81 72 70 93 39 77 Zn 81 67 68 63 69 100 102 84 15 18 17 18 19 22 19 19 4 25 29 35 36 19 21 11 Sr 278 425 421 409 389 452 445 493 V 30 24 23 25 28 35 42 26 Zr 103 103 102 106 134 157 150 117 Nb 7 7.1 6.7 6.4 6.9 9 8.6 6 Ba 203 501 493 529 691 636 694 425 La 0 6 25 23 22 25 13 22 Ce 25 37 23 18 34 36 44 34 Pb 2 0 2 5 0 3 4 2 Th 1 2 4 5 3 4 2 0 Trace-Elements ICP-MS (ppm) Sc 25 26 37 26 V 199 206 305 223 Cr 112 91 12 140 Co 37 37 37 47 Ni 73 51 14 94 Cu 79 80 104 75 Zn 66 78 107 88 26.7 38.3 19.0 12.3 Sr 417 409 469 513 V 24.3 30.3 41.9 26.6 Zr 105 147 173 123 Nb 6.4 7.9 9.4 7.6 Sn 0.90 1.16 1.44 0.83 Ce 0.8 1.3 0.5 0.3 Ba 502 713 654 431 La 11.8 14.9 18.6 14.3 Ce 26.8 32.5 44.2 32.5 Pr 3.7 4.4 6.2 4.4 Nd 15.8 18.7 28.9 19.4 Sm 3.7 4.3 6.6 4.3 1.19 1.38 2.04 1.40 3.8 4.5 6.8 4.4 Tb 0.62 0.76 1.09 0.74 Dy 3.6 4.7 6.5 4.3 Ho 0.78 0.96 1.41 0.89 Er 2.20 2.71 3.88 2.42 Tm 0.40 0.48 0.66 0.43 Yb 2.1 2.8 3.6 2.4 Lu 0.34 0.42 0.56 0.36 Hf 2.73 3.65 4.35 2.93 Ta 0.63 0.53 0.81 0.80 Pb 4.8 5.9 5.1 4.2 Th 3.18 4.06 2.20 1.13 U 1.22 1.60 0.84 0.43 176

Sample HLP9816 HLP9819 HLP9820 HLP9821 HLP9822 HLP9823 HLP9824 HLP9825 Lat. 431450 43.2918 43.2921 43.3176 42.6755 42.6679 42.5711 42.5808 Long. 120.3898 120.3244 120.3233 120.3234 120.0122 120.0056 119.6512 119.5988 Major ElementsXRF(Weight %) Si02 53.85 54.33 48.08 48.32 48.01 47.92 48.49 48.49 Ti02 1.73 1.69 1.72 1.60 0.92 0.97 0.84 0.74 A1203 15.93 15.60 16.93 16.98 17.60 17.34 17.67 17.58 FeO 10.15 9.70 9.82 10.17 9.15 9.65 9.29 7.75 MrO 0.19 0.21 0.19 0.18 0.17 0.18 0.17 0.16 MgO 4.03 4.61 8.18 8.70 9.65 9.26 8.81 9.92 8.33 8.40 10.98 10.14 11.57 11.53 11.86 12.73 Na20 4.14 3.94 3.09 3.20 2.56 2.44 2.54 2.18 K20 1.16 1.06 0.27 0.41 0.24 0.59 0.23 0.28 P205 0.50 0.47 0.74 0.28 0.12 0.12 0.10 0.17

Mg# 49.2 53.7 67.0 67.6 72.0 70.1 69.8 75.8 Trace-ElementsXRF(ppm) 33 28 34 26 35 38 37 34 V 272 206 248 220 239 245 235 232 Cr 39 85 199 229 217 203 248 262 Ni 11 36 117 156 177 161 166 170 Co 110 55 61 78 86 113 115 85 Zn 102 98 82 77 62 66 59 49 20 20 18 15 16 15 15 13 17 15 1 2 2 2 3 2 Sr 464 275 293 305 290 333 257 189 Y 35 48 33 29 21 24 22 19 Zr 143 182 121 126 42 45 54 41 Nb 7.3 9.6 6.9 10.5 2.3 2.2 2.8 6.3 Ba 574 473 134 147 127 150 174 150 La 27 16 17 6 4 5 6 8 Ce 42 49 29 39 9 4 11 11 Pb 0 4 0 5 1 0 0 0

Th 3 3 0 1 0 2 3 1 Trace-Elements ICP-MS (ppm) Sc 38 36 36 V 251 Cr 238 270 304 Co 59 54 52 Ni 187 165 171 Co 94 116 91 71 65 52 Fb 1.2 2.1 3.6 Sr 301 269 202 Y 22.3 23.1 18.7 Zr 48 57 44 Nb 2.7 2.9 6.3 Sn 0.40 0.69 0.66 0.1 0.0 0.0 Ba 126 172 161 La 3.4 3.9 5.4 Ce 9.6 10.1 12.2 Pr 1.5 1.6 1.8 Nd 7.5 7.5 7.5 2.4 2.3 2.0 0.95 0.93 0.81 Gd 2.9 2.7 2.5 Tb 0.55 0.54 0.46 Dy 3.5 3.4 2.9 Ho 0.76 0.76 0.65 Er 2.17 2.23 1.84 Tm 0.37 0.39 0.31 Yb 2.2 2.3 1.9 Lu 0.34 0.33 0.28 Hf 1.28 1.45 1.11 Ta 0.15 0.22 0.79 Pb 1.2 1.1 1.1 Th 0.12 0.12 0.37 177

Sample HLP9826 HLP9827 HLP9828 HLP9830 HLP9833 HLP9838 HLP9839 HLP9840 Lat. 42.8023 42.8098 42.8120 43.0028 43.0570 43.0803 43.0940 43.1316 Long. 119.5114 119.5034 119.5066 118.9479 118.9583 118.7357 118.7118 118.6601 Major ElementsXRF(Weight %) S102 54.38 51.96 51.28 48.29 48.27 47.62 51.14 48.76 Ti02 2.59 2.41 1.79 1.68 2.17 1.13 1.90 1.93 A1203 14.21 14.44 15.22 16.59 16.50 17.81 15.70 17.10 FeO 10.21 12.72 11.46 10.67 12.27 9.96 10.99 9.75 MrO 0.25 0.23 0.18 0.20 0.22 0.17 0.20 0.18 MgO 3.20 4.65 5.87 7.96 6.45 8.80 6.60 7.78 C 6.80 8.30 9.97 10.81 9.54 11.34 8.48 9.65 Na20 3.82 3.49 3.16 3.01 3.46 2.76 3.21 3.49 K20 3.00 1.41 0.79 0.45 0.63 0.27 1.22 0.91 P205 1.53 0.39 0.28 0.34 0.50 0.14 0.55 0.46

43.4 47.1 55.6 64.6 56.2 68.3 59.5 66.1 Trace-ElementsXRF(ppm) 36 40 40 31 33 34 31 26 V 245 381 340 287 326 229 253 211 Cr 17 84 146 242 62 179 122 174 Ni 11 23 43 136 58 144 100 121 Cu 29 187 121 83 86 107 66 64 Zn 117 119 93 95 105 62 94 79 20 21 20 20 20 16 17 18 39 26 9 4 3 1 38 13 Sr 306 389 288 298 327 267 288 382 V 48 36 29 29 37 20 37 32 Zr 128 167 105 103 149 74 138 199 Nb 9.5 11 9.2 6.5 8.674 4.491 13.3 22.1 Ba 2556 490 369 316 382 120 401 264 La 32 9 7 0 4 0 16 14 Ce 40 50 12 10 35 16 29 37 Pb 5 5 1 0 3 0 4 0 Th 6 2 3 2 6 1 5 1 Trace-Elements ICP-MS (ppm) Sc 37 34 42 36 31 29 V 249 322 225 Cr 16 84 145 59 189 175 Co 26 44 40 57 62 47 31 31 47 73 144 116 Cu 37 194 129 97 105 66 Zn 126 126 120 113 69 87 39.7 27.9 11.0 5.8 2.6 15.2 Sr 320 407 311 340 264 416 Y 55.8 39.4 32.0 42.9 20.3 34.2 Zr 143 181 119 162 73 222 Nb 9.9 11.1 9.6 10.4 5.3 26.0 Sn 1.71 1.69 1.24 1.39 0.57 1.71 Ce 1.7 0.9 0.3 0.1 0.0 0.1 Ba 2568 514 374 448 149 304 La 27.4 17.8 10.6 13.8 5.0 20.0 Ce 64.0 41.7 24.9 33.8 13.6 45.1 Pr 9.2 6.0 3.5 5.0 2.0 6.0 Nd 44.6 27.7 16.3 23.6 9.1 25.9 Sm 10.6 6.8 4.4 6.1 2.4 6.0 4.83 2.07 1.54 2.11 1.06 1.85 10.5 6.9 4.5 6.5 3.0 6.0 Tb 1.60 1.11 0.81 1.09 0.55 0.96 Dy 9.3 6.8 4.9 6.9 3.5 5.7 Ho 1.90 1.36 1.04 1.42 0.74 1.15 Er 5.04 3.61 2.96 4.06 1.96 3.22 Tm 0.74 0.53 0.46 0.64 0.34 0.47 Yb 4.2 3.4 2.9 3.9 2.1 3.0 Lu 0.62 0.50 0.44 0.60 0.32 0.46 Hf 3.66 4.85 2.94 3.94 1.69 4.87 Ta 0.61 0.96 0.56 1.27 1.34 1.99 Pb 7.8 6.0 3.5 3.1 1.1 2.2 Th 3.83 2.61 1.16 0.69 0.26 1.69 U 1.37 0.96 0.47 0.23 0.12 0.65 178

Sample HLP9841 HLP9842 HLP9843 HLP9844 HLP9845 HLP9847 HLP9848 HLP9850 Lat. 43.1321 43.1925 43.1925 43.2287 43.2314 43.2345 43.2551 43.2748 Long. 118.7399 118.8192 118.8192 118.7406 118.7405 118.7463 118.7618 118.7110 Major Elements XRF (Weight %) Si02 47.60 51.16 47.84 47.80 47.92 48.07 47.67 48.56 Ti02 1.52 0.83 1.11 1.16 1.28 1.19 1.34 1.21 A1203 17.03 16.50 17.42 17.40 16.93 16.93 17.25 17.01 Fe0 10.47 8.69 9.82 9.92 10.57 9.61 10.29 9.82 MnO 0.19 0.16 0.18 0.18 0.18 0.19 0.18 0.18 MgO 8.58 9.13 8.91 9.24 8.65 9.85 9.09 9.12 C 11.33 9.77 11.70 11.26 11.28 10.91 11.11 10.66 Na20 2.75 2.66 2.65 2.60 2.66 2.72 2.58 2.79 K20 0.28 0.96 0.22 0.27 0.34 0.31 0.28 0.48 P205 0.24 0.15 0.15 0.17 0.19 0.22 0.19 0.18

M9# 66.7 72.0 68.9 69.4 66.6 71.4 68.3 69.4 Trace-Elements XRF (ppm) 34 32 34 34 32 34 34 39 V 271 207 238 231 255 243 244 242 Cr 192 319 190 226 224 337 258 236 Ni 126 189 138 159 139 199 169 170 Co 102 78 98 73 65 57 59 92 Zn 79 65 70 73 77 72 70 73 Ge 16 16 16 17 17 15 17 15 2 23 3 0 1 2 2 6 Sr 243 222 220 232 244 254 252 246 Y 26 21 20 21 23 22 24 26 Zr 78 71 70 61 71 73 87 82 Nb 5.3 5.5 4.3 3.7 4.4 6 5.8 6.3 Ba 218 257 157 289 299 199 160 188 La 16 19 7 10 16 14 3 5 Ce 24 17 6 15 7 21 13 35 Pb 0 4 1 3 0 0 0 0 Th 2 5 2 2 1 1 0 2 Trace-Elements ICP-MS (ppm) Sc 29 35 33 39 V Cr 351 225 343 323 Co 48 54 52 57 Ni 180 139 191 174 Cu 78 100 57 66 Zn 62 71 78 81 22.6 1.7 2.7 2.8 Sr 223 231 273 297 V 21.9 22.2 23.3 27.5 Zr 74 74 81 102 Nb 5.5 4.8 6.4 7.5 Sn 0.88 0.68 0.84 0.92 Ce 0.5 0.0 0.0 0.0 Ba 263 170 200 186 La 8.4 4.7 6.3 6.9 Ce 18.7 13.0 16.4 18.0 Pt 2.5 2.0 2.4 2.7 Nd 10.1 9.5 10.9 12.7 Sm 2.6 2.5 3.0 3.1 0.89 1.03 1.10 1.23 3.1 2.9 3.2 3,5 Tb 0.53 0.56 0.57 0.67 Dy 3.3 3.5 3.6 4.3 Ho 0.73 0.79 0.76 0.93 Er 2.09 216 2.25 2.71 Tm 0.38 0.35 0.37 0.45 Yb 2.2 2.1 2.2 2.7 Lu 0.35 0.30 0.34 0.42 Hf 1.86 1.83 1.80 2.21 Ta 0.38 0.63 0.35 0.51 Pb 2.9 0.8 1.2 1.0 Th 2.39 0.15 0.18 0.25 U 0.75 0.06 0.12 0.14 179

Sample HLP9851 HLP9852 HLP9853 HLP9854 HLP9855 HLP9B5B HLP9659 HLP9860 Lat. 43.2762 43.3228 43.3055 43.2270 43.1859 43.1670 43.1397 43.1578 Long. 118.6866 118.5884 118.5813 118.4755 118.4292 118.4448 118.4443 118.6632 Major ElementsXRF(Weight %) Si02 52.42 47.87 52.37 51.42 48.57 48.74 48.85 47.70 Ti02 1.53 1.46 2.08 1.76 1.84 0.99 0.98 0.82 A1203 16.29 17.23 15.89 16.30 16.75 17.40 17.03 17.46 FeO 9.56 9.96 10.45 10.05 11.42 9.16 9.97 9.38 MnO 0.18 0.18 0.20 0.17 0.19 0.17 0.18 0.17 MQ0 6.28 8.53 5.46 6.56 7.12 9.10 8.97 10.09 C 8.85 11.61 8.12 9.26 10.11 11.33 10.95 11.61 Na20 3.11 2.65 3.24 2.96 2.76 2.70 2.67 2.47 K20 1.47 0.31 1.61 1.04 0.79 0.30 0.27 0.19 P205 0.31 0.21 0.57 0.47 0.46 0.13 0.13 0.11

Malt 61.6 67.6 56.0 61.4 60.3 70.8 68.7 72.4 Trace-ElementsXRF (ppm) 31 38 25 36 23 39 27 38 V 247 266 250 231 260 214 217 230 Cr 87 209 77 70 82 287 314 230 Ni 78 149 65 95 108 156 149 190 63 99 48 56 72 70 69 78 Zn 79 70 105 87 95 63 70 55 Ce 18 16 19 17 19 18 16 14 26 2 32 18 13 3 3 0 Sr 264 254 311 296 321 215 185 200 V 33 26 36 32 30 20 22 21 Zr 156 84 163 124 130 73 65 57 Nb 12.7 6.8 18.1 17 16.7 4.2 5.1 3.7 Ba 487 201 646 388 395 120 141 112 La 10 1 15 28 17 Il 0 9 Ce 23 46 43 47 27 12 23 0 Pb 3 0 4 2 3 0 0 0 Th 2 3 3 2 2 3 1 1 Trace-Elements ICP-MS (ppm) Sc 38 24 33 34 37 V 237 Cr 223 80 318 330 255 Co 57 40 51 65 53 Ni 149 65 155 157 180 Ce 103 49 71 73 76 Zn 79 105 66 74 58 Fb 4.6 35.0 4.3 2.8 1.8 Sr 280 319 230 185 198 V 27.8 36.7 21.9 21.4 21.3 Zr 96 172 80 69 58 Nb 8.2 19.3 5.8 4.6 4.2 Sn 0.90 1.25 0.81 0.44 0.70 Ge 0.0 2.4 0.0 0.0 Ba 222 680 117 136 114 La 7.3 23.8 5.3 4.6 3.9 Ce 17.4 50.7 13.8 12.3 10.4 Pr 2.6 6.8 2.0 1.8 1.5 Nd 12.2 30.3 8.9 8.3 6.5 Sm 3.4 6.4 2.3 2.4 1.9 1.28 2.10 0.93 0.87 0.76 3.8 6.5 2.8 2.8 2.6 Tb 0.68 0.98 0.54 0.54 0.47 Dy 4.1 6.2 3.3 3.4 3.3 Ho 0.94 1.23 0.78 0.72 0.77 Er 2.61 3.68 2.05 1.96 2.02 Tm 0.43 0.54 0.36 0.35 0.38 Yb 2.5 3.3 2.2 2.0 2.2 Lu 0.40 0.52 0.31 0.31 0.36 Hf 2.05 4.26 1.80 1.65 1.27 Ta 0.55 1.62 0.34 0.68 0.44 Pb 1.2 6.3 1.1 1.2 0.8 Th 0.35 2,67 0.33 0.30 0.10 U 0.18 1.01 0,15 0.14 0.10 Sample HLP9861 HLP9866 Lat. 43.1153 43.4467 Long. 118.6233 119.0035 Major ElementsXRF(Weight %) Si02 49.34 47.58 Ti02 2.16 1.46 A1203 16.22 16.78 FeO 12.05 10.97 MrO 0.22 0.19 MgO 5.79 8.90 C 9.36 10.65 Na20 3.34 2.89 1<20 0.87 0.31 P205 0.64 0.28

Mg# 54.0 66.4 Trace-ElementsXRF(ppm) 29 37 V 312 270 Cr 100 227 Ni 68 142 Co 67 92 Zn 101 80 Ce 18 19 F 14 2 Sr 324 217 V 39 27 Zr 151 95 Nb 12.7 7.369 Ba 518 175 La 19 4 Ce 37 20 Pb 4 0 Th 0 3 Trace-Elements ICP-MS (ppm) Sc 37 V Cr 250 Co 56 Ni 151 Cu 95 Zn 86 2.8 Sr 227 V 30.2 Zr 99 Nb 7.5 Sn 0.92 Cs 0.1 Ba 205 La 7.6 Ce 19.6 P 2.8 Nd 13.3 Sm 3.8 1.30 Gd 4.0 Tb 0.74 Dy 4.6 Ho 1.05 Er 2.88 Tm 0.50 Vb 2.8 Lu 0.42 Hf 2.38 Ta 1.27 Pb 1.3 Th 0.24 U 0.11 181

APPENDIX 2: MAJOR AND TRACE ELEMENT ANALYSES OF NON-BASALTS

Seven XRF analyses were performed on non-basalts in thecourse of this

study and are not reported or discussed elsewhere. Methodsare as described in

chapter 4.

Sample 9BJ95 33BJ95 41BJ95 56BJ95 74BJ95 98WHLP98 HLP9B18 Unit Squaw Mtn. Sixteen Quartz Mtn. Quartz Mtn. Quartz Mtn. Hayes Burma (Deschutes C.) Butte (aphyric) (porph.) (porph.)* Butte Rim Major Elements XRF (Weight %) Si02 75.63 75.11 75.17 76.70 76.52 63.94 58.69 Ti02 0.14 0.12 0.10 0.06 0.07 0.88 0.98 A1203 12.99 13.41 13.54 12.87 12.91 16.07 16.34 FeC 1.69 1.60 1.49 1.02 1.06 5.07 6.95 MnO 0.05 0.04 0.04 0.02 0.02 0.12 0.13 MgO 0.05 0.07 0.00 0.00 0.00 1.79 4.24 CaO 0.76 0.88 0.88 0.58 0.60 4.08 6.56 Na20 4.58 4.72 4.66 4.15 4.34 4.59 3.63 K20 4.08 4.01 4.12 4.59 4.47 3.16 2.16 P205 0.03 0.03 0.02 0.02 0.01 0.30 0.32 Trace-Elements XRF (ppm) 112 108 131 142 140 54 48 Sr 50 51 61 28 31 382 399 Ba 1054 1160 919 906 910 874 626 V 54 48 42 46 46 32 24 Zr 197 165 161 120 124 212 124 V 9 6 5 5 4 92 160 Ni 9 8 11 11 10 6 55 Cr 2 0 0 0 0 6 76 La 18 39 30 29 28 20 26 Ce 42 54 42 51 52 52 30 Th 6 8 9 9 10 5 6 Nb 11.9 12.1 8 9 9 9.3 7.9 Sc 5 4 3 3 4 18 20 Pb 15 15 15 19 15 10 6 Cu 9 7 5 9 6 12 58 Zn 70 48 53 52 57 67 67 20 20 21 20 21 18 18 * sample from polylithologic float overlying aphyricrhyolite 182

APPENDIX 3: DETAILED DATA FOR 40Ar/39Ar ANALYSES CONDUCTEDAT OREGON STATE UNIVERSITY

The following pages contain the detailed data, plateau plots, and inverse isochron plots for all 40Ar/39Ar age determinations listed in table 2.3 (pages in same order as listed in table 2.3). Lines plotted on inverse isochron plots are best fit line through selected data and the best fit line withan atmospheric intercept

(36Ar/40Ar= 1/295.5 = 0.003384). 183

1WHLP99

36k11 37kioa 38An(oO 39At5) 40A0(r) Age ±211 40,143) K/Ca±2n

00C178 6000 S 0.03082 1.90269 0,06090 209444 515331 7.07 80.58 36.13 55.87 0,473 .0.038 000179 7000 I 0.00417 2.08123 0,01460 0.97898 1.70708 1.22 *0.32 59.05 18.11 0,140 *0.010 800180 8000 / 0.00100 2.08033 0.00380 0.38135 0.80396 6.66 00.60 75.00 10.17 0.019 00.006 000181 9000 5' 0,00093 1.18819 0.00397 0.18214 0.41149 6.49 01,71 60.03 4.80 0.06600.005 000182 10000 5' 000178 0.55957 000767 0,12554 0,20691 4.79 23,00 2846 3.35 0066 00.008 000183 1205 'C 5' 0.00244 0.73075 0,00627 0.09320 018661 5,78 08.25 20.69 2.49 0.050 00.011 00C184 1400 'C 5' 0,00506 3.43666 0.00975 0.19297 0.51149 7.62 84.16 23.42 5.15 0,024 .0.003

£ 0.04679 11.96041 0.13673 3.74982 9.06263

Information Age±263 39A9(k) Results 40(r)/39(k)±211 MSVIO) K/Ca 0211 on Analysis 740)

S3411pl8 IWHLP99 01)8 Jordan) 269-96 96.1951.4 00.0876 24626 00,28 092 10000 o.oso 50.030 8.4.6.98 whole roolr P466... 03,66% 03.62% Loo6IJon 06190n Eo681,1ot ErrOr0.26 2.45 5609490.11*98 Al*lyOt 66 An&yl)04) Enor 60.26 10000 Error M.9r4906900

Pt6O5 Jordan 1*1.1 Frwloo 2.4116 00.1532 6,95 80.44 7 0.135 00,006 JOadi.900 0302869 Ag. 06.34% .8.36% J58 0,001596 00901.1 Error. 0,44 Standrt 28.04 98roJotioal Error .0.44

2B9.AOE 0>2 IWHLP99Wr(B.Jordan)289-99 ow> Jordan

Ar-Ages in Ma

WeIghted Plateau 7.0803.28 Total Fusion 8950 0.44 Nonred lSOchrsn 7.020054 Inverse ISOChIOrI 70520.52

MSWD 092

I 10 20 30 40 50 60 70 60 80 100 CalnatatiVe 39Ar Reteagad (%)

2B1 AGE 2>> IWHLPI9 wr )B. Jordan) 289-98 ow> Jordan

0.0045 Ar-Ages in Ma

Weighted PI4te, 0.0039 7.088 0.26 Total Fu,orr 6.8000.44 00034 Normal lsootrron 7,028054 Io'ISrSS 960211150 7.0500.52 0.0028 MS7IV 095 0,0023

00017 ,____)

0.00 0.07 0.14 0,20 0.27 0,34 0.4) 0.47 0.54 39Arl4OAr 184

2WHLP97

36A2fl 37A1%2)38kb) 39Aro) 40k)) A86±2* 4,) 39Ar(&) K/Ca ±2*

99C347 SOOt / 0.03415 031560 0.01063 1.51724 4.68315 8.52 00.77 06.45 15.82 2.087 ±0.152 882346 lOOt / 0.04358 0.08683 0,01767 2,34559 7.12583 8.03 00.47 35,58 2497 1.146 ±0.007 990348 SOOt / 0.02358 2.53649 0,01050 2,06333 7.44313 8.25 00.06 51,58 25,99 0.422 ±0.020 902300 900 t 1 0.90475 3.72904 0.06593 150334 4,54741 7.540 0,10 78.10 18.71 0.180 *0,009 990351 lC 0.00135 4.88125 00683± 1,18650 3,12358 7.40 00.12 84,34 12.18 0.107 ±0.006 982352 hoOt 0.05675 125364 0,31334 0,26881 0.49502 5,83 ±0.47 68,05 2.17 0.074 00.003 002353 1200t 084 090364 001704 0.10884 0,22012 5.81 0090 5370 1.13 0,052 ±0003 080354 1400 t 0.06038 5.06740 0.033±2 0.08971 0,25997 7.19 51.75 27,76 1,09 0,008±0.000

L 0.11310 19.60136 0.11662 9.083±3 27.90202

Ago ±211 39Ar(6) Rssufts 4003(39(k)±2* MSWT) ( ±2* On An&ysls (Mo)

Sw9(. 2W111P97 WR 4035-86 ±0.0619 00.28 83.49 2,8057 79 304 5 5 (1258 USSIS 011461000 P8888.0 02.17% 03.06% (.0±59±,, 0168±0 3.18 SIO9SSOOITI090 M2sl EotO,nslEoo,35'20 b8 4681050,1 Ellol 00,11 17440 611±,Msgnikolion

PIqith Joidon *0.0723 Total Fusion Ag. 554 00,28 8 0210 00004 I135 0204*96 2.8081 02.46% 02,52% 0.051536 0,1.1110ElIot±0,28 ShaIxtald 2854 OaMCOIErrol *0.20

4F1$.AGE*0'2WIILP97 WR 4F19-98'00 I I

Ar-Ag.srnMa

W8lrtodP)at.mi 702±026 7±110 FosisIr 8.0400.28 Nonrrsi(±5*46±11 175 ± 024 Inverse(60011,06 775 * 024

MSPIV 3.04

Xlii

0 ¶0 20 30 40 50 60 70 60 90 700 C98144195158 39Ar R.9.ad (50)

*0' 4P15.AOE 2WIILP6TWR4F1548 Jotda8

0 0041 Ar-Ages ki Ma

Welgilted*198090 0.0039 7.9000,26 70198 FusiOn 8,090025 Nonnot1±001*06 0.0034 7.7500.24 (6*80±8)±othron 7,1500.24 0.0028 MSPII) 0,58

0.0023

00017

0.00 0.06 012 0.17 0.23 0.29 0.35 0.41 0.47 39Ar140A, 185

8WHLP97

IflC,86flSflthI 4(t) 36,,( 37j 35jj 39A,c 4((5 Age2o 3(k KJCa ±Ztr

990320 600 t 0.00600 0.24238 0.38436 0.12478 0,38614 6,56*1.53 1043 1,58 0.23100,010 990321 lOot 1 0,38456 0.81554 0.56383 0.44304 0,55056 4,23 *027 32.97 5.61 0.23300,011 990322 SOOt / 0.00372 2.43597 0.00306 1.60698 2.41940 3,09 *0.07 68.44 2r,52 0.389 *0.013 990323 SOOt / 0.00287 2,57139 0.00182 2,86050 3.87712 3.96 ±0.06 81.56 32.95 0.438 00.022 990324 10000 0.00324 1.98030 0,00333 1.50824 230349 3.83 00,07 7527 lOIS 0,408 00.018 900325 hOot 0.80205 1.20247 0.00524 0.77960 1,12162 4.02 00,15 56.07 9,50 0279 ±0.013 990336 1200 t 0,00394 0.55594 0.56354 535005 0,54273 4,25 01.19 35.01 4,07 0.175 00,028 880327 1480t 0.06409 6,26170 0,56413 0,37152 0.63138 4.7800.43 34,25 4.71 0.02600,401

L 0.03213 16.00502 0.02781 7.68480 11.43052

Ifliarmagen Age±205 39k(k( 696 R..±It. 40(r(/39(k(±22 MSVST) (((Ca±2o AnalysIs (Mx) (%,n)

Sompe 65*41697CM 005.rsIo 4614-95 W.iget.d 00.0204 00.11 1.4219 240 6012 0262±0094 10±4.031 p105909 *1.85% 02 66% 150500cr 0,9090 External Error* 0.11 4.30 SIAbSIlOalT1080 530je.l 84439954854500.07 .4207 Error M55n190490n

Project Jordan 14497000258 00,12 InSd(090rl 081)4696 ToSal FoMoo Ag. 01.70% 4 0294% 8 021200.000 4-yoSt. 0.801503 ExtentS Error *012 Steflderd 28,04 93*50031Error * 0,07

4F14.AGE'0' 8WHLP9T ONseparate 4F14-9$0*'Jordan

7* * Ar-Ages IsMa

WeIghted Plateac 3 98± 0.71 Total Foorr 4.0000.12 NornroI I500lrrorr 3,9300.12 lnv*0co .0*5109 3.9350.12

MSWD 202

& 00

0 tO 20 30 40 50 60 70 90 90 100

C.nIo4jn. SOAr R.I.a.ad(00)

4F14.AOE'*45 9WHLP$7GM Separate 4F14-9g500Jordan

0,0345 Ar-AgeskiM.

Weighted Plateso 0.0039 3950011 Total Fu9.o.r 4.06 ± 0.12 Nontral teootrron 00034 3930012 (no.505000*5509 3,93±012

00028 MSWD 0.00

0.0023

0.0077

0.00 0.12 0,23 0.35 0.47 0,50 0.70 0,82 0,94 39Ar I 4OAr 13WHLP98

1(1) 39(k) 360a0037A0o51 38Ar0l 3OArO 40M0 A921* K/Ca±21*

960445 500% 0,00385 0.42600 0.00015 0.00233 0.18*88 22.71 05.17 14.02 4.24 0.075 *0.004 590448 700% 0,00008 0,25434 0.23 0.04406 0.25544 16,45 0*60 1001 2,45 0.074 60.004 660447 500% / 0.00117 038200 0,00009 0.06525 019716 6.43 6104 3625 462 0106 *0,006 960448 000% / 006033 0.54207 0.00013 0.21050 0.45165 5.88 60.39 0480 11.74 0.167 *0.009 900449 40080 / 0,00071 425420 0.00037 0.26525 0.52453 5.40 00.34 7097 14.78 0066 *0.005 660450 1100% / 0,l9 1.40088 0.00030 0.25473 0.50435 540 50.40 69.60 14,19 0,073 *0.004 950451 4200% / 0.47 141519 0.50202 0.36050 0.79080 5.49*0.25 6424 24,19 0,008 60005 990402 1455% 1 0,00452 0,41515 0.80683 0,52952 1,08001 585032* 73,47 29,48 083500062

X 0,01514 12,33033 001022 1,79624 3,97243

nfarrn.tIon Age ± 215 39Ar/k/ R..ults 40(r/l39(4, ± 215 MSWD K/Ca ± 215 oe Analysle (MO) (%.n)

San1* I3VIHLP9S 01 4E1648 2,0246 5,56 1,17 0060 60026 M6I00*1 041*15 lOck L*03020 O,8o*n 0*1611151ElIot60,22 2,07 S189650011 1650 6064,40 35 MMybssI 0*415*015 40605 01,1* MagS80660

2,2125 5,07 * 411% 8 0.063 * 0.002 1194460*. O*U4F86 '4*184 4o46o5 Ag. J-*615* 0,004524 E,5I0,4810t,or* 025 SI2*00d 28.04 001610S661 0102 6 0. 40

I4F18.A0E ,OotI3WHLP88 wr4Flg-983315 JonIan I

Ar-AgesrnMa

W15glltod P495.00 5.50 ± 0,22 104*1FoSioll 6070025 NoosSi )eo64.00 5.4200.28 3061*5150*111*1, 5,4000.28

MSWOI 4,17

0

4

2

0

I 10 20 30 40 50 60 70 60 90 100 CUfl50IiltI08 3gAr R.Iese.d (56)

4F18.AOE I3WHLP98 wr4Fl$-88003 I Jordan

0.0045

0,0039

00034

00028

0.0023

0.0017

I Into I 0.00111

I 1151 I

I IOregoo I

I Ib I 002061 I OSLJ4F9O I

10.001524(J) I

0.00001 J 000 005 0,16 025 0,33 041 0,49 057 085 3M, I 40Ar 187

15WHLP98

Age ±25. 40Ar0) 3() 37A!15)38frgh 39A.50) 40J() 3(91 1

t0l3 600 t / 0.60292 .59256 000562 0.56611 0.57760 534 0045 4010 721 0.125 00017 0001014 lOOt / 0.60116 2.56319 0.00120 0.57963 .96254 5.29 .0,33 79.57 13,56 0.110 *0.014 I0l5 SOOt 1 0,00076 3.00751 0.56074 0.60306 1.25561 5,24 40,07 54.71 15.89 0.090 .0.012 1OI6 9000 / 0.75 2.72000 0.90176 0,73130 1.30632 5.44 00.43 8627 17.11 0,116 *0,014 0001017 I000t / 0.59169 2.54626 0,00361 0.90211 1.25012 5.25 00.54 66.69 15.44 0.112 *0014 l0l6 hOOt / 0.90271 1.97024 0,56529 0,59527 0.86660 410 .0.45 512* 1229 0.115 00.030 6901019 1200t / 0.00417 207302 0,01906 040256 090262 483 8156 35,65 945 0064 *0.047 *001020 14000 I 0.56706 9,66233 0.00646 029280 0.59633 5.16 02.52 24.99 6.60 0.017 00.004

L 0.02139 2556606 0.03464 4.27516 7.75714

kifo,meflen 399th RsesIt. 4059/3906 ± 2. Age ± 2*. MSWD 1

S*.,ple 5094LP94 WO (9. J56dSfl( 2910-1 W.4g1h1.d 19456 *0.0632 5 40.10 0.37 100.59 o.000 o.034 8110+0100+. P186.69 03.43% 03.49% 0 L00000., 0.65011 0,5*2081 05640.15 229 0140.60817 rsHo 59 4*460602* 56 80.16 1,5600 0056 M.0.9o.8°

6515601 d80 7.485 P48500 Ag. 15145 5.17 6 0.073 80.568 304+0800 0002546 0.001502 01456.10356 4033 SlOfld9ld 28.04 4*8*0602* 056 00.33

2B10.AOE 0150ISWI4LPB WR(B.Joma.$)2B10-99 00390161

Ar-Ag.shi Ma

WeightedP18*880 5,2600.10 Tot81 Fosloil 5,11 00.33 600111851900+1100 5.2700.25 (n08156Isothroo 5280025

MSWD 037

01 0 10 20 30 40 50 60 70 80 90 10 085.614813. 39*, R*4.md (19)

ZB1O.AOE 25656I5WHLP9S WR(B.Joida.i)2B10-19000 Jordan

Ar-Ageshi Ma

W.ightadP185602 00339 5.26±0.16 Tot85Fooios 5.1100.33 No.5*4(±od.ro.h 00034 521±025 (556.06(900+1,011 5.2800,25

00028 MSWD 041

0.0023

00011

0,00 0,09 0.19 0,27 0.36 0.45 0.54 0.83 072 39*,I40A, 24WHLP98

Inouem.nt.I 36(±) 37Ar(oo)38*7(5) 39*7(0) 4Ok(r) Age ±2n 401)3*) K/Ca ±2ro

990454 SOOt 0.00811 0.15751 0.00181 0.08817 0.28500 20.35 ±4.33 10.85 124 0.008 *0.005 950158 700t 0.00300 0.40507 0.00172 0.07887 0.28108 7.55 01.18 10.50 210 0.070 00.004 950458 000% / 0.00315 1.97511 0.00220 0.00519 0.88950 5.98 00.43 41.54 5,83 0.058 00,004 900457 500% / 050258 341504 0.00202 0,03932 1.12829 9.08 ±0.21 55.18 20,80 0.080 ±0,004 900455 ¶000% / 0.00272 2.73725 0.00335 0.72075 1.54488 5.73 00,15 55.58 23.94 0.119 ±0.008 990459 5*00% / 0.00340 2.95380 0.00734 010229 1,28557 5.87 *0.22 582* 19,00 0.088 00.005 090150 1200% 0,00485 *10*29 0.00553 0.25532 071930 7.58 ±087 34.33 5,40 0.088 00.003 990481 1400% 0,52214 11.75959 0,50875 5,41435 141752 9,50 00.97 ¶7,50 13,45 0,015 0 0.001

0.05008 2523*45 010073 3.07315 7.58505

Ag.±2o 39*7(k) RSWSS 40(r(/39(k) 2211 MSWD K/Ca±215 08 AnalysI. (Mo) )%,rl)

24081LP90 WO 4F17-90 W.IØ,5.d 2,1582 00.0840 *024 2.39 427 18.18*185 w*oi. rooll P805..o 0258% ±4.04% 039* 00015 L000955 0r*on E0580181 Error 0024 3,15 018909*81 r±90 882*98 s.r8*v*looIErro.o°'7 1.5353 E*rorMagn00090n

boo. (5:::;8 7±5.0 F0510rr 8g. 2.4970 8,73 0 0,052 00,201 0,001514 E,n*errsl Error 0025 Standard 25.04 taw011osi Error ±0,15

*0> I 4F17.AOE >0, 24WHLPI9 YdR 4F17-98 Jordan I

Ar-A9.. *8 Ma

Wegtrted 085595 5,99±0.24 105±8 F00ion 6.73 ± 0.26 Norrrr±8 l.00trrorr 5.73±0.01 Inoers. ).odvon 5.7800.62

MSVOD 230

ro 20 30 40 50 60 70 80 90 100 CanraI.tIv. 39Ar RsI.a.46 (50)

*0> 4F17.AOE 24WHLP9 504F17-9$5"Jordan

0,004! Ar-Ages (or Ma Weilrted 0.5.95 05039 5.89 ± 0.24 10*85 Fusion 073 ± 026 Nonrrr85 teoolrrsn 0.0034 5.7300.61 )fl0 (800*0001 5,760062

0.0028 MSWD 3,23

00023

05517

000 008 015 0.23 0,31 039 0.46 054 0.62 39Ar14OA, IL3

25WHLP98

Age 405%),) 3957)6) 36 3757/03)3857/95 3957)) 4557(1) x,±±211

000384 SOOt / 0.03742 1.79634 0.03149 1,16415 0.03273 807.4±¶05.8 5.36 53.75 0,446 ±0.040 000385 700 t / 0.01175 2.17257 0.01327 0.80539 020311 880.8*1834 9.02 2320 0.150 *0,014 002388 SOOt / 0,30931 4.14385 0,96804 0.96198 0.16908 702.5 *247.0 829 ¶6,15 0.090 *0005 002387 SOOt / 0.00049 0,77310 0,00088 020443 0.03748 ¶802.9017732 20.51 1.57 0.030 *0,003 093380 ISOOt / 0.0*152 1,18085 0,96291 0.08015 0.0±077 1*008 01214.0 0.98 2.31 0.02000.0*3 00038* hOot / 0.96081 042005 0,09580 0.03088 0.01017 758.4 03183,4 5.32 0,89 0.032 ±0,004 000370 1200t / 0,30120 2,41502 0.00008 0.42588 0.02084 2417.0*3878.4 7.77 0.86 0.005 00,000 37l 400 t / 0.001 13 3.47218 0.00003 0,02482 0.01588 ¶524.5 *7113.7 4.40 0.72 0,003 *0001

0.06043 1830337 0,0580* 3.47134 1,15784

IntO7fllStIOfl Age ±2* 3957(0) 08 AnalysIs R.sults 40(1V30/k)±2* MSWD K/Ca ±2* (09)

0050. 25W541P88 064 2021.09 WMghSd ±0,0483 MsI.5S 03682 *117.3 ¶00.00 0.0*8 *0007 51-5049(596 P3sj 1175.76% ±15.8.0% 5 LOcon E*OI ±117.4 2,36 SleOsocal rra8O 411_st *,ns 04 411±59*91 ErrOr 0118,8 1.0000 011±1Ma9n9*a0ol1

P1q5*1 Jordan 00,0663 ±¶43.8 *9.3000* TOtalP.4.105 *34 0.3338 8081 8 0903096 *7.78% ±¶7,64% 008* ±0005 J.*.0* 0.00134 0*10103)000 ±43.0 Standard 28.04 M,Iv9C±I Error ±113.3

2E21.AGE I 25WHLP98 GM 2E21-89 Soc Joidan I

Ar-Ages 105 Ka

W.rØ1t.d Pl±teao 740101*7,3 TosI Fosron 806 1 0 ¶43.8 50,004/60*10,08 461.1 0520.6 inverse(50011,00 467.0±354,6

100700/ 0,87

5

/000

500

0 0 10 20 30 40 00 60 70 80 90 100 C9884l501v83941, Releasad (30)

0" 003 2E21.AOE Z9WHLP98 GM 2E21-99 Jord83

0.004T Ar-Ages m Ks

WSØlt8d P191±16 00039 740.1 ± 1*7.3 7±1.1P481±11 800.7 01438 50,1581(s003roo 0.0034 461.1 ± 526,6 lflVOf5O ls0010lOfl 4610±354,6

0.0020 1005502 058

11±.-11--

0.0 0.5 1.1 1.6 2.2 2.7 3.3 3.8 4.3 3941,) 4OAr 190

25WHLP98

37Ar(oo) Age±211 4)307') 3)4) 36.00) 3630/4) 3930/r 4OAr(r) K/Ce± 255

900356 SOOt 000607 010519 0.00483 0.28742 0,07904 0.59 *0.59 2.59 9.74 7.519 *0.043 990*07 700t 0.01602 0,55062 0.0126* 0,72209 0.37070 1.56 00,36 7,25 2*20 900368 loOt 0.526 ±0.010 0.01153 1.90099 0.01106 075756 0.63414 252 ±059 980390 lOSS 2729 0.201 ±0.006 SCOt 0.00647 2,51865 0.00727 0.54003 0,56041 1.84 00.37 14.66 lOSS 5.552 *0.003 900398 1500t 0,55235 2.70175 0,553*5 023074 010274 34 ±0.51 12.84 640 990391 1100 t 00*7 00.001 0.00005 290950 0.00190 0,10854 0.14107 3.92±lOS 3595 990392 3.90 0.053 00.001 1200t 0.90049 5,71205 0.90082 020780 027850 7.35 03.19 10.37 1,55 0953 *0.801 980393 I400t 0.05222 5,55578 0.00114 036238 095000 0.00 *0,00 0.00 3,05 0.005 00.060

) 0.04890 17.151*4 0.04337 2.74054 1.57309

biteomatlon Age± 211 393090 Oh Analyst. Results 40)r)/36(k)± 21, MSWD K/Ca±2s5 /48*) )%,fl)

S*nn,4. 2OWHLP9*or 557.98 Caviot M9I 000 wOrds rook C*I054±6. (.00±805 0,8055 87±05903)1 r±00 3.3)1,97 5*05197 Error 0191000±/Error Color 4885,400*5071

Prepot Jordoo 5±9.90. Total P.61004g. 04095 0,0774 7040023 0035600 012,75% 072,75% 6 0.009 ±0007 J-*±kOS 0,00187* Eot.rrlSl Error *02* 57±03614 28.04 ±0.1090*' Error*023

5E7.AOES's2SWHLP9 wr 6E7-ltlt '00 01616 I

Ar-Ages in Ma

WliQlltsd P7*05±0

705*) FoojOn 1,54±0,23 50,70*) Io001rlon

Inverse Io000ron

485780

&

2 10 20 30 40 50 80 70 80 90 700 Cumulative 3M6 R.9..Md (%)

5E7.AOE 00> 25VAOLPIS wo SET-IS sos Josdas

Ar-AgesinN.

W6)tirtod Pl.teuo

tote)F0000 5.54 ± 0.23 NOflIre) 5000,05

/595155600017,08

483850

0.0 0.5 1.1 7.6 2.2 2,7 33 3.8 4.3 39Ar040Ar b

I

I

8

uuu 8

8 I 8

I g 81 Il HHHH w

8

9p,p,p999 8 2 : :; 1111 hi .ey 192

48WHLP98

3eArlo) 37Ax(80> 38.4z(d) 39A,lk) 401 Age ±21, 4OAs9 39(l

990482 80OC 4' 004152 0,18066 001470 0.00548 2,82593 9.84 81.52 18.71 8.80 1.936 983483 700C 4' 0,00088 0.45028 0,02750 1.88350 5.18751 8.20 *0.59 32,16 19.00 1,799 990454 800C 4' 0.02900 0.94292 0.02425 1.85349 5,17810 7.90 *0.07 38.36 20.32 0,891 990465 9000 4' 0.00991 264941 0.00580 1,58023 4.49595 7.54 *0,12 61.38 17.54 0.274 963406 1000C 0.00166 2.60536 0.00446 1,26915 324073 7,61 *0,11 68.61 1320 0.209 690487 1100C 0.00088 1,94337 0.01193 0.73210 1,83215 7,46 *0.19 97.29 7.61 0.192 990400 1200C 0,00192 1,38433 0.02293 0,54627 139144 7.00 oO,28 70.79 5.67 0.169 900460 1400C 0,00839 5,09140 0.04319 0.66964 1.91410 8.27 *0.28 90,41 717 0.060

2 0.12690 15.75562 0.15826 9,61499 26,08091

Infonnatlan Age±2ro R.sufls 40lr)/39k)±2o MSWD YJCa on AnaIy.ii (Mo)

50P18 48WHLP9O WO 569-98 W.igtss.d 26721 00,0649 7 00.19 2.06 68434 0,342 Mot.r181 o.trote rook P181899 02.00% 2.41% 10*840,1 Or000n E88921 Ema0.19 3.18 5189880011 858 Anoly56aI0,10100.16 1,4309 Errol MogWboolorr

P8900t Jord*n T0184P1rs48# 2,7110 00,0783 *0,25 8 0,282 tn*,ào8 o5U5E98 Ag 02.89% 03.15% J-ook,. 0.001665 EOtOlrot 519200.26 Sloodold 2694 AooOtOai Ens, 8 0.23

5E9.AQE>0% I 4$WHLP9$ WR 6ES-øl 0%' Jordan I

Ar-Ag.s in Ma

Waightod P00880 7,96±0,19 Total Fos,o0 8,09 ± 0,25 Normal lsochron 7,77 ± 0,24 Inverse lsochron 777 ± 024

MSWO

6.0

ito 0 10 20 30 40 5,0 50 70 80 90 100 CamoIattva 3GAr R.le.s.d (%)

5E9 AGE 0%> 4$WHLPI$ WR 6E9.0 0%> Jordan

0,0045 Ar-Ag.. In Ma

WeIghted P56880 0039 7.7500.29 Total Fosion 9.08±0.33 0,0034 Normal Isochnon 7,51 ± 016 "N " 'N, InverSe5009600 7,51±016 00020 'NN N MSWI) N"' 1,47 0.0023 N 0,0017

000 0.06 013 0,19 026 0,32 038 045 0.51 39A,I4OAr 193

74WHLP98

37±) 38*6(0)) 39*6(14) 40*6),) Age ±2:1 40k75 39*6(k)

090420 600% 001032 0,00200 0.00064 0.51716 4.54810 609 00,40 33,65 461 2.417 ±0.147 090425 700% 0.04*79 1 0.74223 0.03684 3.06173 0.73370 7.65 ±0.20 3020 28.70 4.769 *0.006 900430 600% / 0,03424 4.68423 0.03776 3.14111 5,70565 7.54 ±0.30 48.62 2920 0.862 00.047 ±90434 675% 0,00733 1 221676 0.01102 1.05044 4.73303 787*0.11 08.44 45.41 0.345 *0.010 900432 950% / 0.00133 381309 0.32400 .44587 4.15351 7.77 *0.10 91.05 3.44 0.103 *0.008 800433 1*25% / 0.00030 I649900.305*6 0.65475 4.86539 7.5800.17 5467 562 0.136 00.0*7 990454 4400% 0.00011 0.97936 0,01162 0,45*60 0.36046 0.77 00,57 9220 1,45 0.099 00.0*5 550435 4250% 0.00*24 0.4*923 0,01555 0.06029 0.00534 324*4.20 5722 0,75 0.360 00.066 0*0436 4400% 0.00059 3.99657 0,75 0.40020 0.40645 5.43 04.46 40.54 0.03 0.011 *0.004

t 0.09760 10.46003 0.15253 10.75882 30.34750

Info,m.tlon Age±24, oil AnalysIs R..uIt. 40(,(/39(k)±2:1 MSWO K/Ca±25 (49±) (%n)

50440* 766LP80454*4718-90 W&g0I.d 6560(94 2.6727 *0.030* 715 *0.25 266 92,07 0.476* 8484940*14 P4±496± 24.35% 03,49% 0.124 2020* 0,690,4 9*0*9) E0*, *025 2.76 34±800*31 104(0 0*8144.4 08 8±34y4(03 E4II41±0.40 4.6349 0148049834400*0*0

Pr40c4 jo,4. 70494 Puolon *0.28 1418*46600 2.5470 *0.0536 761 9 0.299*0.007 0554F96 Ag. 04.00% ±3.46% I-09(03 0.0*1001 ExlOTnOI 0:1*4*0.26 04±4*3rd 2354 0044446 0410,*0.14

I 4FSIAOE>00 74WHLPIlW4F18-98'00Jordan

Ar-Ag.6 In Ma

Wei4t8d P1±4800 1.7600.25 1*4±) FuSion 7.810 0,26 9045494 )500llSos 1.590 0.29 7.7600.28

2.68 I

Air.

C596594a65. 30*4 R94nas.d (00)

4F18.AOE0±04 T4WHLPI WR 4918-98'0>Jordan

0.0845 Ar-Ag.. In Ma

02039 W90,48d P19489* 7.7600.25 1049 FuoioIl 7.67 00.26 0.0034 9*550)1500144*5 7.69140.29 (nooI690 0.0028 7.76±0.29 490000 3.94 05023

0.0017

0.2011

0.0808 0.00 0.06 0.12 0.47 0.23 0.29 0.39 0.41 0.46 38*0440*44 194

76WHLP98

38k 37k)o.)38Ar(d) 39Ar)k) 40k(r) 40A/(r) 39AJ1k) K/Ca ±2a (Me)

990396 60270 013240 005378 000105 001354 0.00000 000 00.00 000 3.67 0.108 00.015 990396 75270 025999 0.44980 080470 009397 000000 000 00.00 000 2542 0.09000.000 990397 00270 033936 227013 000000 0.00000 0.00000 000 00,00 000 000 0000 00.000 99C390 1050 C 047832 549409 0.00453 0,15397 23,8)925 376700103.72 1442 41.67 001200001 990399 1260 '0 0.49201 2.01030 0.00130 0.06033 7,71345316.54 079.60 5.14 16.34 0,013 0.001 990400 140270 0.12974 161680 0.00034 0.04765 2.55744144.54044,32 6.63 12.90 0,01300.961

1.81682 11.89380 0.01193 0.36926 34.19017

kifonnatlon ± 39Ar(k) Results 40(1(139(k)±2rs Age 2a MS(AV K,a ±20 on Analysis (Mo)

76WHLP98 Plo9 5016-08 Caalot 000 Mot.rllo orr-.rorrdrr600 031051.1. L000loo Or.goo Eotrrr) Error 01.0090.1190)0 lor&y.t An&yOo.) Error EnOrMo5ro600Uon

P90.01 Jo.rt.n Tat.lPo.lo.. 920929020.9062 23493049.24 6 )rmdote. OSUSE96 0g. 022.25% 029.99% 001300000 0.0015 Eotorrr&Errmy49,25 Stofld.rrt 28,04 An)0yt44) Error *44.95

5DI6AOE >5> I so, T6WHLPIS Pug 6016-98 Jordan

Ar-Ages InMa

Weighted P).ta.o

Tots) Fos)on 234.62±49,24 Norma) )soctrrofl

(flyers. )sochron

MSWO

& 4

50

00

50

0 0 10 20 30 40 50 60 70 80 90 100 CUmuI.ttv. 38k Released (%)

>5' 5016AOE 7SWHLP8 Plag 5016-98 'so Jordan

Ar-Ages InMa

Welgtrtad Ploteas

Total Fosion 234.62 ± 49,24 Norms) (socirron

)rrvarsa )soctrrOn

MSWD

0,00000001200024 0.0038 000480,0060 0.0072 0.008400097 39Arl dOAr 195

76WHLP98

nt.I 36AUO) 3llf(os) Age E2 )') 38A5(d) 39A5) 400.5,) K/Ca±211

090304 8560 035178 0.21673 5,35975 0,00421 0,46852 2.86 00,43 7.44 *4.70 1.000 00028 050357 lOOt 0.00708 0.51618 0,0*354 0.68488 0.43524 1,04 8025 172* 08030$ SOOt / 19.38 0,554 00.0*8 0.00592 1.44031 0,01548 0,74*08 0,21085 1.06 0020 090300 SOOt 13.35 2*61 0213 00.058 / 0,00350 2.03635 0.0*150 5.08490 5*8244 980380 090 00,22 *4.73 17.46 0.096 *0.003 l000t / 0,502*4 2.97035 0.50990 0.36407 0.10572 0,65 0033 1423 *0.75 0.063 00,002 89038* 1*5010 / 0.05*40 2,37462 0,00853 0.23490 0.1*654 ¶47 50.48 2191 890382 ¶30010 6.87 0.043 00.08* / 0.00281 4,78558 5,50028 525473 0.59395 0,98 00,41 10.12 8,35 0,006 00.00* 950303 *40010 / 0.055*2 2,57067 0,00002 003136 0.0*343 1.270386 28.52 0.92 0.005 20.000

L 003090 17,90104 0,07403 3,42938 175485

Inform.tlon ge±2 3902)0) on Analysis R..ults 40)*)/39)8)±211 MSWV K/Ca±2o (M8) (%,5)

0osç19 76WH0P80 0,50*0,08 W819h1d M919051 o.os 00*469 5, 0014 6582 011-2*. 501* p1.8.9± 0*3,79% 0*3.85% 0088 00000 1.00090,, 0mqofl 2,57 30101/sI ExIesual ElIot 0014 01980943171000 30,oS000I Enot 0014 1,0952 Elm, *2.914804800

JoIdafi *00414 0*0209011 tOtal P01904 44. ha0012 osu0000 0.487* *5.32% 0042% 8 oosz 0000, 0.001840 on 00*2 014,509,0 28.04 2098*304* Eon 00.12

I SEIO.AGE115*VSWHLP9I wr 5E10-99 0*' Jordan I

Ar-Ag.. *6 Ma

W6*ghtnd P19*690 ¶5* ±5*4 totalP01906, 1.480012 Nosmal I.005roo 085±075 floe,..)sod*ron 0,08±0.50 usw0 1.21

01

.01- ) ¶0 20 30 40 50 60 70 90 00 100 C9n5u1.tl0. 300., R4l..nad (10)

6E10.AGE 0" TsWHLPee wr $E1O-955%'Jordan

0,004! Ar-Ag.. In Ma

W91t.d /198800 0.0039 1,0* 00,14 70891 FoalOn 1.4600.12 Nom,061.008106 0,0034 0.85±0,70 InverSe*5408,0,, 5,66±0.55

0,0028 MSWD 1 28

0.0023

0,0017 \.. "-

0.0011

00006

0,00001 -I' 0.0 0.5 1.0 1.5 2.0 2.4 2.9 3.4 39 390., 8 40A, 81WHLP98

Age ±2*5 36A496) 37k)58) 3845339) 44)r) 40k),) K/C9 ±2*5

000248 800CC 1 0.02788 0.50034 0.0*458 0.58170 0.44396 *97 0053 5.10 1230 0.604 *0.041 000249 700% 1 0.02468 090331 0.58635 0.40744 0.33502 2.26 *0.75 4,36 8.00 0,19000.016 000250 600% 1 0.01771 0.59731 0.90351 0.25110 023289 2.55 1.19 4,28 4.97 0,122*0.0*0 000251 900% / 0.02061 1,15048 0.00628 0,33731 0,39705 2.51 01.13 4.78 0.87 0 026 0.010 000252 1 0.0*675 It 0633370,00693 0,27484 0.22*05 2.22 01,51 3,84 5,44 0.042 00.0*2 000253 1100% 1 0.02*54 0.66982 0.02*36 0.89874 0.6094* 2.00 *0.66 9.36 *7.55 0.228 *0,022 000254 1200% 1 0.02082 9.35*02 0.04947 2.17994 1.13051 1,43 *0.28 *5.52 43,13 0,100 *0,008 000255 *300% 000*46 130751 0.00*30 0.0860* 00007* 02* 0735 *53 I76 0.028 50006 000256 *400% 0.00014 0.66638 0.5*06 0.00580 0.00000 0.00 00.00 0.00 0.1* 0.026 30.119

X 0,15369 *5,6*934 0.10983 5,05341 3.33659

Information Ago±2* an Anslyal. R..uft. 40(r(I39)k)±2* MSWD K/Ca 2*1 (Mo) (%fl)

Sanr% 5156ILP958I2SI4-gg W3SIII44 o,3o3o *0.31 206 95,12 Matins 5*43.100k **7,76% 0*7.77% 0*34 *0043 0155011 EXSrnS ESorOOSI 2.45 0590500* 1*090 3401501 MOtIOnS 550100,3* 1,4357 50101 M03980090.I

P*oI TO55*FIsIoo *5090900 0,9903 00,0963 182 *0.27 9 0SU2899 0*4,50% *4.60% 0126 00007 00100*5 0.00*527 EXISIrmI E501 0027 StaMOld 25.04 410},90a1 0,101 *025

I2B14.AGE55>8IWHLP9Iwr2BI4.gg3010 Jordan

Ar-Ages in Ma Wnt,ted P)atoa* 1.7400,3* Total Foson 1.820027 Nomlal1.400,55 1.30± 0.34 )flVe*08)9000,Ofl 1.30±0,34

MSWD 2.08

14

2

0 10 20 30 40 50 60 70 50 90 100 Canmlofs. 3M, ReIeao.d (%)

2B14.AOE on> 81ILP$8wr2B14-gI son Jordan

0.0045 ,j Ar-Ages In Ma Weogilted509*600 0,5335 1.74±031

1.82±0 27 No,nral.0*9650 0,0034 1,30±0.34 )nvors.l000tnoo 1.3000,34

027

::::

00006

0.0000

0,0 0,3 0,5 0.6 1,1 *3 1.6 1,8 2,1 38A5140A, 197

103 WHLP98

4094(r) 3994(k) 3AAr>n>3794(co) 3894>oi> 3994(k) 40kg> 'N) K/Ca ±215

002682 600C I 0.00022 2.02018 0,00841 0,40034 0.51231 4.92 *0,28 92.59 21.22 0.098 80.010 000583 700C 4' 0.50033 4.42911 0,00417 0,42793 0,71503 4.59 *0.45 89.07 20.17 0.042 00,004 002084 8000 4' 0,09029 4.738060.00197 040102 0,66443 452 00.62 89.06 18,90 0,036 *0004 00C985 990C 1 0.00017 1,94606 0.50107 0.19590 0.33096 4,61 1.50 87.07 9.23 0,042 80.004 002596 1000C 1 0.00026 1.74320 0,00178 0.17037 0,23519 3,77 *2.38 75.43 8.03 0,042 00.000 002087 12000 4' 0.00092 6009430,00418 027879 0.48715 4,88 *204 6461 1314 0.02000002 502584 1400C *' 0.00074 12.12443 0.00116 0,19720 0,54434 7.52 *4.08 71.21 9.30 0,007 00.001

2, 0.0029033.13657 0.02375 2.12138 3.79041

information R.sufts 40(r(/39(k)±2r, Ag.±215 MSWD 3994(k) K/Cs ± 210 on Analysis (MO)

S.nrl. 1O3WHt,P98 WR 2815-90 Wdght.d 1.7550 *0,0766 478 *0.21 0.90 100,00 0,014 00.011 Ma10414 04,04.10,4, Ploleor. *4.38% 4.45% 7 Lo.*000 Oraqon Eololn,4 ErrOr 00.21 2.45 0509.9.141,0,90 69 Anolyllool ErrOr 00.21 1.0000 Error MOgrO8u.brar

P69005 .JonJon T011 Fo.to. 1.7910 00.1909 489 7 0.020 0.061 Irr.rMSorr 005)2899 89. *11.10% 411.18% ±0*108 0,001514 E.tOroO) Error .0,56 099,48,4 28,04 Ana)yl50al Error 00.04

2BILAGE 'os IO3WHLPUWR2BI5-99 000 Jordan I

Ar-Ages in Ma

WOight.d P508946 4.79 ±0.21 Total Fusion 4,85 2 0 55 Norma) (0009rofl 4,60±0,50 (flVOlSO )socflroo 4,63± 0,46

MSWD 080

44

24

10 20 30 40 50 60 70 80 90 100 COfl90i.tIo. 3994 Rei.aa.d (%l

2BILAOE 9>> IO3WHLPI$WR2B15-9a >3> Jordan

0.0045 Ar-Ages in Ma

Wnighied P)at,nu 0,0039 4,79± 0,21 Iota> Fusion 4.89±0.55 Norma> 150141,05 0,0034 4.60±0,00 )soctlron 463±0,46 0,0026 MSWD 100

0,0023

00017

0. 001 1

0,00 0,09 0 19 028 0.38 0,47 0.57 066 376 3994)408, 123 WHLP98

36At(sj 393.ç05 39 Aoo±2s 4O0(r/ 39A K/Ca ±2.1

880329 60070 099441 0.26903 0.99295 0,12496 0.15639 3.88 *0.75 10.65 10.31 0360 *0.009 990335 70070 0.00242 0,89997 0.96220 0.14341 0.19596 3.40 00.60 18,74 11,83 0.080 ±0.002 98033% 80070 1 0.00776 343991 5.09*4% 0.26577 5,19977 2.09 ±0.45 26.91 2123 0.53% *0.991 950332 80070 1 0,90697 6.26040 0.08073 0,35090 0.27050 2.27 5,35 49,13 28.94 0.024±0.00% 990333 100070 0.00076 1 .89527 0.90140 0,13188 0.12401 2.75 0073 75.76 10.88 0025 *0.001 990334 110070 0.96061 1 0.89641 0.00293 0.07611 0.06790 2.24*193 ¶9.39 828 0,047 *0.001 990335 ¶25070 1 0.96053 1.12134 0.00408 0.96006 0,06655 2.45 *1.74 25,59 6.60 0,53% ±0,003 950335 140070 1 0.06037 6.31099 0,00101 0.03939 006101 5,06 ±583 42.40 3.20 0.003 00,099

L 0.01200 21 18383 0.01697 1.21218 1.11069

Infassnutlon Age±2.1 assAnaIy,8s R.**lt. 40(14/30/k)±2o 359) K/Ca±2* (M9(

Se*42 123WHLP86 WA 0911.96 909499596 *$1020 *0.30 7788 M&21121 0.7806 230 141 o,00s±0,004 504545 61.922.. ±¶3.06% 03.73% 8 O*so E3124n21 0.1101±0.30 2.57 $1893902171960 6±9102% 69 M±IoSO.I ElISI ±030 .1882 EssMsç9±96±0

66±4814 .105150 ±0.0969 75921F±±400Ag. 0,9162 270 ±0.29 Is±d5900 osusa s,o.sn ±1066% 9 5525 *0.008 J.volIn 0.061834 £51211181 90*1±0,26 51*11.6914 2954 45409903/055*0.29

5DII.AOESEE123WH1.PIIWR SEll-ag " I I

Ar-Ag..9. Mi

028406664 P00±9± 230 ± 030 75994 659.5.1 2.70±029 54055594(1.045.081 22250.89 208 * 075

540042 1.4l

'K'

I 70 20 30 40 50 60 70 80 90 100 CUm1819846.39kReli8asd (00)

SOlIAGE >0'> 123WIILP9EWR SEll-ga '3*1Joilasi

0,0045 Ar-Ag.,(us Ma

05819989461.5689 00039 2,30±030 70*21 F±9on 270±029 Nor5021 15014111*8 59934 2.22±0.99 (608159 (90141100 2.08 ± 075

00026 M$WD 7.63

00023

00017

00 02 04 0.6 09 II 13 1.5 17 34A,l40A, e

ii

! ! c

I' h I I h

e H HE

iI C H 0 I

A

0'U P9PP?P9' p h H JI!J 130 WHLP98

Incsum.nt.I 40011(5 36A7(6) 37Ar(±o 38Ar(d) 3959)5) 40A7)) 8 3997(1,) K/Co 2 211

000222 600*0 / 0.00002 1.15194 0.00241 0.16520 0.14873 2.17 ±0.64 000223 1426 ¶549 0.060 ±0.005 700*0 / 0.00112 1,65652 0.06064 ±24370 0.10088 2.16 ±0.60 3721 20.36 0.063 ±0.005 000224 800*0 / 0.00006 1.80244 0.56060 0.2±461 0,15657 1.50 ±0.66 31.40 16,64 0.006 ±0,804 000225 088*0 / 0.00117 170405 0.00140 021620 000809 ¶20±135 2160 000228 1000*0 16,06 0.06400,804 0.56053 0.66736 0,00118 037663 0.80050 035 00.00 000227 1150*0 0.00 6.41 0.000 *0,005 0.00105 0.56601 0.00126 0,07267 0,00000 0.00 00,00 0.00 8,06 0.065±0.013 000228 ¶305 *0 0.00366 7,16000 0.00308 0.16417 0.06778 1.10 0303 040229 5.57 1330 0,010 ±0.001 1400 *0 056001 0,00879 000000 000000 000000 ¶094±000 000 0.00 0,000 ±0000

E 0.01179 14,77672 0.01110 1,10544 0.54004

In9ormatiOn Ago±2± 065 A.s.Iysl R..,ft. 40sV39 ±2± '(') K/Co±205 (1,10)

S018 I3OWHLP9O 012616-99 W.lghI.d 07269 ±0.1497 ±0,41 73,61 08160*5 107 1,01 0,060± ot,o10,000 6163.60 *20.54% 020.54% 4 0007 .30800.1 Or.000 Exteoni E00r ±041 3.16 SI058900I7 1890 b8 01101,00810110.00.46 1.0030 5118. M.gnlO±840n

08105 00.2405 186*5990.1 1054160*500. *. 0,5350 146 ±0.65 0942895 ±44.03% ±44.02% 6 ±035 ±0002 J-089J8 0.0015 0±5411.) 5±0.55.55 SlOOthod 08,04 9081090315001 ±0.65

2B16.AOE 55.1I3OWHLPI8wr2BIS-g9±5*5 Jotdan I

Ar-Ages hi Ma

W61g)1t.d P101601 1.9700.41 10091(109105 1.45 ± 0,65 90001*5150811100 1.7000.84 Insane IsoxhroO I 52±0.78

640880

0 10 25 30 40 50 80 70 80 90 100 Com.oI.tIoe 39A, R.Ieued (%)

2B1,AGE so' 130W84Lp9$ WV 2B1849 '>' Jordan

0.0045 / / / / Ar-Ages InMa We,ç4ded P1±06.0 0.0039

0.455 0.65 - NOmlal(60810100 0.0034 1'700rdroo 1,82±0,78 0.0028

00023 N 0.0011 N

0.0011 N

0,0008

0,0000 0 0,0 02 05 01 0,9 1,1 14 ¶6 18 36Ar (4059 201

138CHLP98

36Ar(.> Age 37A1(03)38A,1> 39A1(k) 4ft4j),( 401 39> K/Ca±2n

000394 800 C 0.00602 2.42437 0.00004 0,06003 000305 750 0 0.71443 19.03 19,98 3.01 13.31 0.015 90,002 0.06106 7.00330 0,00049 027328 000390 0,08021 0.08 312 044 41,97 0.017 00.002 8500 0.03352 2.57607 0.00004 0.12347 000387 960C 0.33843 0,35 03.28 3.30 18.96 0.021 .0002 0.03794 088945 0.00010 0.04883 0.45253 23.25 50,20 000389 1200 0 3.98 1.04 0.520 00.008 0.05102 3.57341 0.00108 0.10278 000389 164242 36.70 3294 9,82 10.78 0.012 0.002 1400 0 0,01436 10.27394 0.00000 0.01810 0.77823 92,15 14,30 15,58 2.93 0.001 00000

3. 0,2643028.83134 0.00271 0.86100 4.01625

Information Age± on Analysis Results 40/1)139(k)±23 23 39Ar(k) ± (MO) MSVSO K/Ca 23

94.OPIO 138WHL088 3M 2E23.99 048,05 6.010401 0.00 0110(0root, 0.1001.6. .008800 O,.qon 060,1,81 Error 394000311,000 AnoIy.t 68 6n81090.(5,101 Eno,MOgnIt±0900

Prn100I JOrdon 10181 F0ul00 1,194010,1 6,1688 02,5747 1425 05.92 0302098 Ag. 041,74% 041,61% 0 0.011 00,001 ±08(00 080*266 ExtOrnO(Er101oS,93 01.ndd 28,04 AnolySnel Error. 593

2E23.AGE 8>> I3SWHLPØS GM 2E23-99 >>s Jordan I

Ar-Ages in Me

Weighted Plateau

Total Fusion 14.250593 Normal (soohroo

Inverse lsoChron

MSWD

'04 ii 0 10 20 30 40 50 40 70 80 50 100

Cun*slotlr,8 29*6Released1%)

2E23.AOE 0>> I3SWHLP9BOM 2E23-99 so> Jordan

00045 Ar-Ages in Ma

Weightnd P1818.0 0,0039 Total Fusion 14,25±5.93 0,0034 I Nonnal Isocirron P InverSe )soolrroo

0.0028 MSWD

0,0023

0,6017

0.0 0 1 0,2 0,3 0,4 05 39Arl40A, 202

145CHLP98

,nhal 36kb)37k)9±) 119±20 38A7(ol) 30k(k) 40k),) 40),)3)6) K/Ca±20

990490 0000 0,00507 5,28201 026570 044472 049315 3,36 ±5,45 902497 700 22.10 8.49 0.729 ±0026 0,26733 0.71148 0.01000 5.53±97 962490 0,79705 2.82 ±0.21 21.09 1561 0.002 *00,9 C / 0.26790 2.40919 0.01062 1.47907 .03973 2.10 ±0.12 30.15 28.09 000499 900t / 0.263±2 0284 ±0010 5.45295 0.0±557 1.44092 1.04929 090500 2.22 ±0.00 53.03 27.41 0.114 00,004 bOOt 0.0±078 4.47754 0.00394 0.64917 0.36934 1.84 ±0.17 8225 1225 990501 hOot 0.00044 0092 00000 1.08393 0.00271 0.21667 0.12198 890502 1200 t 1.72 ±0.50 4792 4.12 0,068 ±0002 0,0±023 0.61448 0.50142 0.39194 0.04162 980503 1400t 1.50±128 37.87 1,56 0007 ±0002 0.00000 0.57157 0.00102 0.11510 ±15172 3.66±1.60 40.33 2.27 0±05 *0000

0.02611 25.18292 0.04809 5,25649 4,05308

lnfern.aiIon Age±2o on Analysis Result. 40(b/)39)k)±2o MSWD 3OAx)k) K/Ca 222 (Mo) 1%,,) S±n,4± 14508LP98 W9 525-80 2651981.4 0.7206 50,0226 220±0,07 Sb101Sh008 PIehaso 03.16% 03.30% 0.66 0104±0102 L00980., 2 0100101, MebyM Exb.,nel Efl., 00.07 12.71 0t98090)T,000 815 40015128)11,05±0.07 1.0260 110±, Me9rl5oa±.,,

JOlden T0IJP±.IonAg. ±00269 230±0,09 0325285 0.7712 0349% 360% 8 o,es±o,0o2 5±01695 EXternal 11,101±0.09 Standard 2804 daeb800.IErnoo±006

SE$.AGE 03> 14SCHLPIO WR 5E6-N

Ar-Ages In Ma

Wetghted PlShes* 2.20 ± 0,07 10851 FUSIOn 2.36 ± 0.09 Noon51 5025,00

Inverse IsodIron

MSWD I 0.95

0-i

0L

50 50 50 70 50 90 100 C966.itIV. 3SAr Released (56)

E6AOE ,*o 1UCHLP99WR 5E9-98 90 Jordan

0 0041 Ar-Ages In Ma

00519111.4 P045.9* 00939 2.2000.07 15551 F48ish, 2,3600.09 NOmId 50±8110,, 00034 no.150 5005,05

0.0026 MSWD

0.0023

0,005/

0.0 0.2 0.5 0.7 0.8 5.2 1.4 18 1 9 39Ar140A, 148CHLP98

kIC09I9S9OSI 36Ate) Age ±21, 4OAr(r) 37Ar(±±)38Ar(d)39000) 4002(r) 30) K,C ± Zo

900470 900*0 4' 0.01070 0.10990 0.90091 0.05905 0.90518 32.00 ±5.27 900471 700 *0 1 9,83 77 0.144 ±0.055 0.01279 0.83013 0.05048 0.13495 080318 99±472 1534±1.73 1549 4,10 0.30100003 800*0 4' 099734 1.72003 0.00018 0.30217 1.14487 9.59 ±0.78 34,50 *428 000473 800*0 4' 0.00000.003 0,00799 4.41492 0.00005 0.80414 2,18300 900474 *000*0 8,23 ±0.22 4794 2400 0,078 ±0,053 1 000928 3.09082 028020 0,70500 2.02594 900475 1100*0 8.7* 0029 42.4* 21.9* 5593 55063 1 00*454 1,60464 0.99112 0,51240 4,870*7 9.88 ±0.58 2798 15,02 0.137±0.000 900470 *200 *0 1 0,01557 0.91833 0.99*83 024789 *28520 *2.52± 99±477 *400*0 1.07 *82* 775 0.118 ±0.004 1 0.01318 70*495 0,00805 5,30425 1.30405 15,71 ±5.71 22,58 *225 002400,00*

L 5.40248 *0,558*5 0.0*278 3.2*782 *0.7438*

Infoom.tIon 095 Resull. Age ± 2o 39Ar(s) AnalysIs 40(r)139(k) ± 2o K/C± ±21, (84±) MSWD

09*054. I4800LPO0WR 500.08 2.9259 ± 0.315* 8450104. 40090,049 Error P540.32 087 ±0.96 3770 *00.00 ± *0,77% ±10,61% 8 5048 50557 Lo0±bon 01±5±. *099*6 EoIe,rel Ener 2098 2.38 04±9±850 7*580 58 404*8550501±00.05 8.1300 0.0184430803900

33388 T0t±IP±9looA. 10.12 8 0.07*00,00* 0,05*604 0±4.01±1 Error *025 S*On*J.*d 2804 540*51*06 Error 00.22

$E8.AOE'0±S4ICHLP9WR5E6-91"0 Jordaer I

Ar-AgesI. Me

15*44505)00 10,1200.20 Non,*& Is000roO 7.0300.25 *30*55600015± 7.54 * 026

NS05V 37.70

1 10 20 30 40 50 60 70 60 00 100

C±msl.tio. 39*, Rele.s.d(50)

9E6.AGE300I46CHLP9SWRSEll-ge'So Joodsos

0.0045 Ar-Ages mMs

0,0039 Weighted P148090 0.9702,99 10044 FU0180 10,1200,20 02034 P4or,n44l±Osh,50 753±026 1000109lsoCt*rofl 7,54±225 0.0028 MSVOO 053 00023

0.0017

0.0011 I SampleInfo IWr

0,0006 N lbs N IOSU5E9B

'N, I0001684(J)

N I 0,0000 0.00 006 Oil 017 023 028 0.34 040 045

SOArIdOAr 204

HBA-3 (Streck)

Intel 36Ar(o) Age ±2* dONS) 37Ao.) 38Ar(W 39A1(k) 4ou 3W) K/Ca±21,

000352 605 t 0.51739 0.651370,60975 0.62051 1.87051 000303 700t 5.74 0,39 25,60 5,64 0.606=0.055 1 0,01178 1.17089 0.00593 1,46054 2.99553 000354 5.51 00,16 45.43 6.95 0.536 *0.047 600% / 0,01333 .09499 0.00794 267575 5,45794 5.36 *0,13 59.07 ¶7.63 0300 *0.055 500355 905% / 0.05559 3,00211 0.01155 4.21338 7.83785 5.26 *0.29 000356 975% 49.88 25.83 0,5*6 00.056 0.04083 2.02540 004217 2.81063 4.28101 000357 464 *0.41 26.22 16.01 0.553 50.050 025% 0.05393 1.45173 0.54934 1.39398 250494 5.05 *0.90 13.58 6.54 0,413 *0.048 005388 1100% 0.55229 ¶98344 0,57423 1,49351 3.63744 8,44±1,25 1352 9.16 0.394 *0,035 000358 ¶200% 0.60355 6,11944 5,21255 1,56856 3.51537 7,75 ±310 ¶0.87 6,74 0,077 *0,004 360 ¶300% 0,02132 1,84024 0.07659 024301 0,77202 8,97 *2.96 10,92 1,46 0.06* 80,012 000361 140* t 0.60040 0.0000* 0,00056 0.60125 0,00000 0.00*0.00 0.00 0.01 0,000 *0.

E 0.3514920.28264 0,49848 14,31030 3236223

Age ±2* R.sult. 40(1)728(6)±2o, MSWV K/Ca±2s

San,ge 86A-3 w.*4tn.d *5,5847 ±0,19 tMle,i0 544 378 52.42 o.sao oo,o52 etWer009 Pt.tesu 53,36% 2343% 3 L0o*bon 0,95*8 ElelonIEooeSO"9 428 91.1.959111990 *4 90*501)04 Eoo, 00.16 I 9455 611*1M094409920

Ploleol Jordan Tow FUsion IIna<*.Uon ¶9793 00.6074 5 0028 06*0649 44. *4,93% *4.97% ¶0 0.346*0.017 V2)*t 0,001549 001.1581*1101*0,28 Sl*od&d 28.04 NIy9caI ErrOr*0,26

I2811.AOE5*39 HBA-3*395JOISt510

Ar-Ages55U.

Weghl±dP1*58.4 12 5.440019 1055 Fools., 5.5900.28 NoflIlsi 1900hr011 10 501 ± 0,55 Inverse Is551lr*n 5.020092

MSWD 378

6

¶0 2 30 4 5 8) 70 90 90 100 C58l54l.t155 39At Rlte*6.d (%)

2B11.AGE SOs. HBA4 5*39 Jo1dan

00045 ArAgsltMs

Weighted PIeteaO 00239 5,4450.19 101*5 F000n 5.55±0.28 0,0534 Norn.a1 /6*55125 5.0100.55 noons. 1.005,05 5020053 0,0028 N MSV9D 1,90 N, 0.0023 N 0.0017

00011

'N 0.0059 NN N 0.0000 000 0.09 0.17 028 035 043 052 080 069 39101040 ziJ,i

HBA-13.5 (Streck)

360,).)37k(88) Age ±2o 4001),) 38k(sI) 39k(k) 4001(l) 39Ar(R) K/Ce ±21,

0000995 800 0 / 0,05577 1,16620 0,05402 1,40952 3,56509 0500916 799C / 7,06±142 17.73 25.87 O.5ll±0,159 002145 2.39074 0.01030 1.05559 2.99495 0000967 800% / 7,46 *0.31 31.42 2801 0.205 ±0.025 0.00725 2.07690 0,003±2 0,85413 2.30041 0000998 600% 775 ±0,27 5229 15.74 0.177 *0.021 0.90545 2.45672 0.00573 0.81569 2.03023 0000859 1050% 8.97 0018 59.73 15.03 0.143 *0.011 0.00538 3.88371 0.01173 0.74462 1.82193 8.85 ±0.24 53,39 13.72 0262 80.010 0001000 1100% 0.00515 2.33541 0.01213 0.35413 0,98492 0001091 3000 779 *044 39.30 6.55 0,065*0,008 0.00516 8.10881 0.00758 0,14974 049832 0001002 9.31 *3.01 24,84 2,78 0.008 *0.002 1400% 0.00034 0,54784 0,00031 0,01351 0,12339 25,45 ±52.40 5904 0,25 0,011 ±0.002

2: 0.10585 2237772 0,07563 5.42722 1426524

Inferm.tlon A84 06 ASSlYSIS R.esIts 40(1Y38(k) ±20 ± (945) MSWD (0/Ca 2*

Soar4. \-13,5whd4,008)8.J0,d38)2811 W.4911t.d 990531* 2.7149*0.0725 *021 81.72 whols ,±sit pl.I_* *2,97% 094 0192 *0.050 0100041 E,00181 Ewes *021 4,38 S1e98800(1 teSs 4038.1 88 fleItOOe( E,,6100,2O 1.0006 80*194830355*0±6

PIqest J0, 00,1471 9,541*0*11 T5to1P58(se 959 2.6285 7 50,41 0502099 560% 05,84% 8 0102*0.017 0,001500 E*t.,ne( East 00.42 Standard 28.04 Malyt*5( east*0,41

2812.AOE±42,HBA-13.5 whoge .ock (B.Joeden) 2812-ggEs,Joiden

Ar-Ages in Ma

Weighted Ptateeu 7,60±0,21 Toll Fusion 7.36±0.41 99,4,1* (asdesso 7.81 ± 0.46 Inverse )sOcIrrviI 7.67 ± 046

9,5000 0,84

1 70 20 40 30 50 60 70 60 60 100 CUmstletlne 3601 ReleaSed (00)

2B12AOEEs, HBA-13.Swholerock(B.Jodan)2B12-gØ'Es r4I591

0 0 Ar-AgesinMa

We0hted p150.00 00039 7.60 ± 021 'Toll Fosion 7,3600,41 Nownefls008ros 0.0034 7.8700.40 Inverse (sodtr*n 7.87 ± 0,46 00026 MSWO 0,00

0.0023

0.0017

000 0.06 0.12 0.18 0.24 0,31 0.37 0,43 0.49 3IAII4OAI i I

0 S

HIb IHbI i ,t I Iii H 0 [1

I S

S

:1 = I HHH S :'

Ui 'a

J S S g 00 B i 1111 ;hI ivoplivst 207

HLP-98-12

36k/a) Age ±213 40Alr> 37A2(0*) 38A1(ol) 39Ar(k) 40k/rI K/Ca ±2o

000205 400C 1 001006 069273 0.01008 0.79993 000207 7080 1.62124 5.96 *0.22 30.28 28.18 0.497 *0.030 I 0.08821 1.60394 0.30839 0.79892 000208 6600 1.50502 6.87 *0.37 39.65 28.18 0.214 00.017 1 006567 336600008614 555517 000209 9000 1,38067 5.76 *047 43,97 2453 0,089 *0007 I 0,30236 215904 0.00329 0.27585 0.48877 522 000210 1000C 1.16 42.90 9.71 0,004 *0004 I 000083 0,83365000256 0,00434 011764 060211 367 0406 3245 332 0,049 *0006 12000 000017 0,50162 0.00104 002080 0.00000 0,00 0000 000 1,06 0,026 *0010 000212 1400 0 0.00266 6.33470 0.00181 0.14242 0.21722 4,49 5,70 32,28 5.03 0,011 *0,001

3; 0.02991 14,52547 0.03398 2.83923 540299

09058041 Results Age±2o on Analysis 4O(r)/3S)k)±29 MSWD K/Ca±213 (Ma) (%,n)

0a*'5r)e NLP.08-12 ±o 286-99 WaIghud MeleO.l 2.0638 00.0583 500*0.18 392 9393 whole005 Pl.t..9 02.91% 297% o.oso eo.044 L0088orr Oregon Eoterrrel E *0.18 2.76 St.b.90el 1900 Analy.t bg 60.6166 Er,wrOO,ll 1.0000 Sf0,MaOf9Soatlrel

P10101 1*6.0 T8telF4slOe Inodteoon 18030 00.1278 560 *0.38 00U2800 Ag. 06,71% 06 7 o.o84 40.004 J-oeloe 0.001634 601.666113600.06 SIOfde,d 28,04 AnslySoot Enol 00.30

286.AGE>5, I I4LP-88-12wy286-99>0>JOrdan

1 Ar-Ages in Ma

Weighted PleteslI 5.60±018 Total FoSion 5,86±038 Normal (SoChron 5.12±128 Inverse lsoOhrOfl 516±126

MSWD 063

CUrmlieltne 3SAr Released (%)

2B6.AOE>5>HLP-98--12wr286-I80>,Jordan

00045 Ar-Ages in Ma

Weighted P1.1.4* 5.0835 5,5000.16 Tote) F*Siofl 5.00 ± 0,38 00034 Norms) loohnov 5.12±1.28 Inverse lsochroo 5.16 ± 1,26 00028 047 00023

0. 0017

0.00 0,08 0 17 025 0,33 0,41 050 058 0.06 3500140A0 HLP-98-24

Age 39734 37(1 38A34)39849) 4(5P70) 4r9397 KCa±2rr

000240 8O0C / 0.00289 2.68402 0.00151 0.18290 5.49197 7,85 00.80 36.51 15.10 0.030 00.002 00C241 703C / 530038 40)067 0.00206 0.25157 5.63565 7,14 00.77 85.58 21.29 0.028 00.002 000242 6000 / 0.00027 4,57151 0.00000 0,31849 076490 6.99 00,91 90.0 26.37 0.03000.002 000243 1002C S 0.00058 3,34315 0,00070 026968 0.64555 6.51 01.33 7894 23,60 0.037 00.000 960244 1196C / 0.00044 0,84476 0.00046 0.07460 0.10010 3,92 05.40 43.73 6,16 0,038 00.008 900245 1200CC / 000535 0.92912 000032 004110 003676 2,54 01418 2562 3,40 0,01900006 000246 1400C / 0.00089 840256 0.00000 0.04805 0.04709 2.69 017.06 15,21 3.80 0.062 00,001

2 0,00579 24,76616 0.00299 121176 2 71808

Information ± on Analysis Results 40(1)/39(k)±20 MSWI) 39849) K/Ca±20 (Mo)

SerW4e HLP-00.24W62B7.89 W.lgl.t.d 24721 ±0.1481 721 *0.43 100.00 M.10r131 op488 P8300.o .5,69% 0001% o.00e oo.00g

Or.son 50101118*Error 00.63 2.45 01.9.60311660 An,1101 59 Ar58yrj)5 00.48 1.0000 Error Mogr49o.6on

P101001 JsrrMn 16831 F88*oe 22414 .0,3460 654 01.01 159d.60n 0032689 Ag. 015.53% 01551% 7 0,021 00.001 0,001621 EoIOm& Error 61.03 Olosd.rd 2504 An.1(t±.I Error 61.01

I 2B7.AOE 0>> HLP-V$-24 WR 2B7-89 >34 Jordan I

Ar-Ages In Ma

Werghtod P18*600 7.21 00.43 10*9) Fo5i65 8,34±1.01 Norm.) )sodrron 6.8900.59 108108)500*rron 6.92 ± 057

MSWD

01.

0 10 20 30 40 50 60 70 80 90 100 Co6WIstIrmS9Ar RsIo0.ed (%)

2B7.AO 34, HLP-N-24 WR 2B7-98>5±Jordan

0.0045 Ar-Ages In Ma

Platoco 0,0039 7.21 ±0.43 Tot.) P05165 6.54± 1.01 Norm.) )900hrsn 0.0034 68900.68 )nv.o )50s*rroo 6.92 ± 0.57 00028 MSWO 034 0.0023

0.00)7

0,00 007 0 13 0,20 0.27 034 040 0.47 054 39Ar I 40Ar 209

HLP-98-32

Intel 36k±)37Ag(oa) 3AAt(o 39A,(k) 4Ag() Age 22,1 4082(r) 3(11) K/Ca ±2*

0001539 SOOt 1 0.00413 0.27870 0.00075 0.17175 0.94840 ¶5.75 00.95 43.88 8.50 0,265 ±0.363 0001539 lOOt 4' 0.00364 0.59247 0.00084 0.25543 .30805 ¶5.48 00,80 5926 975 0,199 ±0.117 0001540 SOOt 1 0,30343 1.19856 0.00047 0,30183 1.71201 15.17 00.88 62.71 1228 0.087 40.019 0001541 SOOt 4' 050390 3.40930 000004 5,43252 225804 499 00.83 6625 1648 0094 *0009 0001542 10000 4' 000577 4.96488 0.00001 0.54299 2.90877 ¶5.54 00.02 63,39 20.72 0.947 00.008 0801543 ll00'C 1 0.00471 2,46105 0.00004 0.37171 1.87818 4.43 *2,47 57.41 14.18 0,065 00.009 0801544 1200t 4' 0.00298 0,08604 0,0*000 0.1777* 028096 12.09 08,85 5*23 6.78 0,000 ±0.000 *001545 1400 t 1 0,00225 0,0*000 0,00023 0,34732 1,06072 1388±8,71 71,64 1325 0. ±0.

E 0,03050 13,31406 0,00239 2,02094 1364417

infOrnhitlon Results 40(r/'39(k)± 2* Age ± 2* MSWD 39*1)11) K/Ca ± 2, on Analysis (Ma) (%.n)

S.n,çS. HLP.80.32 5480±10.. 2012.99 00.1591.4 53784 ±01320 1534 0036 043 ¶00,00 070,516 ±0707 M81806 01109,0±11 P18K.0 5245% 02.54% L00390n Orason 058109 Coor 00.30 2,36 S1a9092.It 1050 800041 06 949105*.) 0,11000.37 1,0000 01101M±0I5110090n

P10041 JolSon 1±1.1 P5.10* Ag. 5,2050 14,55 0 0.065 50,096 111.31.90* 0502896 J.04100 0,001588 FXl.1I'SI ElIot ± 1,38 St9nd.ld 20,04 94±110*81 ErrOr ± 1,37

2E12.AOE900*HLP-9S.-32plagiocls.2E12-9g'*5Junta.

Ar-Age. I. Ma

Weigirted P1.1.0± 15,34±039 1*18 FusiOn 14,85* 1,38 10*559)1800111*5 14,78± 1.08 )nversO)s0±hron 147901.00

MSWD 0,43

10 20 30 40 50 60 70 80 50 100 Cumuistive 39A, Released (00)

2612.AOE*2*HLP-95-32plagiocises2El2-992*.Jordan

0,0045 Ar-Age. in Ma

WeigiltedP10)8±9 15.3400,39 00*39 TOt. Fusion 14.85±1.30 9015,84teodrr** 14.76±I 08 0,0034 147981 08

MSV9I) 0.0020 0,20

0.0017

0,0011

00006

0,00001 - _I 0.00 003 006 0.09 0.12 015 0,19 0.22 025 36A,I40A, 210

HLP-98-33

m.ntaI 4041(r) 3(a) 371,,(06)345*)39fr5k1 4fr,,() A06±20 3941(5) I(1C4 ±2*7

990439 600'S 000327 006300 0.06173 0.06016 0.16543 2520 07,29 14,84 0.60 0.137 30.065 690469 700'S 0.00334 0.26804 0,00293 0.04675 0,35213 1224 0,26 29,30 2.66 0.132 00.005 000440 600'S 1 0,00299 0.99786 0,00329 0.37157 0,64888 7.80 9042 51,70 11.14 0.160 00,007 990461 600'S 1 0.00153 1.46273 0.93 0.43314 1.10291 7.86 0025 70.71 12.69 0.126 00.065 690492 1543'S / 0.04069 1.41587 0,06628 0.04124 1.46161 7.63 00.20 8454 17.73 0.180 *0.006 960463 Il® '0 / 0,00073 1.13330 0,00067 0.55303 1.30745 7.57 30.23 85.94 '660 0.210 00.006 990494 1200'S / 000060 073042 0.00095 031646 0.76432 7.5930.35 81.35 8.56 0.166 00.007 890495 1400'S 0.40166 11,99325 0.06999 0,66797 2.00310 6.07 *0.19 30,63 23,72 0.030 00.801

5 0,01525 16.02045 0.02092 3,39095 6.07613

1057.68906 Ago±211 on AnslysI. R.suII. 40(rV39(k(±2*, MSWD 39Ar(9) KJCa±2o (50) (%,n)

64'nclo HLP.90.33WR 503.90 WeIghted 2.4073* 0 68,02 68*1.49 wtros,00i, p150.0 01.60% 7.68 1.12 0.162 00.000 L092bon Oleson Eol8o,.l 61,0,0015 2.78 553*303)11*99 02,0160 94 9231,3002573000.12 1,0567 E,r0r64858190990

Project JOrd*fl 00.5373 0835900 OSUSE98 TOW 6*509 Ag. 2.8011 0143% 8.03 9 0.080 00.002 2.301715 Eolelr8IEIror00,15 81315018 28.04 4381,40*1 Errot 90,11

8E3.AOE505 I HLP-98-33 WR 5E3-99 s's Jordon I

Ar-Agas hIM.

W019h16d11)010*4 7.90±0,15 70*4)F4*.00 8.03±0.14 1,06,05 I600hrofl 7.54 ± 0.22 056769)880*050 7,54 ± 0.22

MSWD 1.12

LiZ I

0 10 20 30 40 50 60 70 80 90 100 CgrrlUI.lIoo 384, R61....d (56)

5E3.AOE sos HLP-98-33 WR 003-98 sos Jo.d.n

0.0045 ArAgel In Ma

WeIghted P1.1.89 0,0039 7.88± 0. 15 181*1FcsIOr, 8.03 ± 0.14 1,8805)80010,011 7 54± 0.22 05018618000,80 754± 0.22

:: MSV9I) i\ 0,45 0,0023

0,2017

0,00 0,07 013 020 027 0,33 0.40 0,47 0.53 394,, 40Ar 211

HLP-98-35

38k(,) 37Ar(eo) Age ±261 40A114 Hasting 38Ar(d) 39A7(k) 3gkkl K1C±20

000014 900C 1 0,06406 1.44234 0.01676 2.33978 13,47505 1707 90.88 41.50 41.78 0,606 00.174 560575 10010 / 001782 2,25548 000384 0.98228 552735 16.88 028 6048 1754 0 186 0 018 000518 6000 / 0.00142 2,44156 00607* 058402 332500 1857 9545 68.75 10.61 0.100 00.010 000517 000C 0.98095 4.53576 0.00204 0.80769 4.89227 15.88 *0.38 9461 980518 *621 0086 *0,008 100010 0.00072 2 57639 0.00393 0,34594 1.89140 *6,21 01,16 80.87 6.18 0.055 00.006 080019 118010 0.00120 1.21476 0.00412 0.17298 089521 1514 *292 71.31 3.08 0.081 50.012 800580 *20010 0.00140 1.17102 0.00147 0.07203 0.41326 16.82 08.40 49,50 950081 1.30 0,027 00.010 140010 0.00650 18.94184 0.00334 0,19446 0.99303 15,080513 34,08 3,29 0.005 90,001

008851 32.59315 0.03621 5,59990 81.39696

Information an Analysis Results 4059/39(k)±21, Age±20 39Al1k) ±20 (Mo) MSWI) K/Ca Sanpi. HLP-08-35 810 285-90 Wlghtad Molmial 5,6202 90.0774 18.80 90,25 0.51 88,93 0,126 00.065 plOts.. *1,36% 1,50% 3 Lao9tOn 0*6899 Ao.IyOl 08*0*6.1Elror *0.38 420 0109.90,11 r.O0 59 An&*500I 5915190.23 1.0000 Poor Magnt6o.ton

55900* Joot,o 0o895os1o6 1*941.008 *0,1510 1502 50,48 0002699 A9 8 0.074 00,000 JOOO 92,60% 02,15% 0,001651 596094 Enoro 0,54 5*54598* 29,04 An.lySe.l 5061 *5,45

I 2B& AGE 000 HLP49-35 WR 2B6-99 000 Jordan

Ar-Ages in Ma

Weighted Plateau 16,6800.25 Total Fusion 16,62 ± 0,48 Normal lsOChrOfl 1649±0,46 Inverse (sOctIron 18,49±0.47

MSWO 0.51

C96OuIatIVs395, RaI,05sd 1001

ZBLAGE>341HLP-95-35 WR ZBS-6± >>> JoSdan

0,0045 Ar-Ages In Ma

Weighted PIOte.0 0,0039 16.71 00.24 Total Fusion 16.6± ± 0.39 0,0034 No9l ls000ron 16,46 ± 0,44 InverSo Is005ron 16,48±0.44 o 0028 MSWD 019 00023

00511

000 0.03 006 009 5,12 0,15 0,16 021 024 39Ar I lOAn 212

HLP-98-40

Iflerem.fltil 40 38A1).)370joo)38Ar65) 39Ar)k) 40A0)l) Ag± K/CC±261

0001540 6000 1 0.00302 1.25989 0.03705 0.47499 0,22609 1.40 *0.37 19.80 6.37 0.162 .0.368 0001547 7500 1 0.00144 6.42644 0.54761 3.03111 1,27180 127 3Q13 74.71 40,03 0.203 .0.034 00C1549 9620 / 0.00127 4.37106 0.01072 2.27009 0,81605 1.16 30.16 70,00 30.65 0.224 *0.038 0001549 1000C / 0.00080 1.90359 0.00383 0.47534 013237 0.84 00.86 34,34 6,37 0.108 *0.019 9001550 1200 0 1 0.30300 129187000820 055380 002800 015 0306 3.06 7,41 0.183 0.946 0001561 14000 0.00733 1064915001578 064011 000000 000 00.00 0.00 5.66 002600533

001691 25.92700 012320 1.45960 2.53030

InformatIon ±210 ResUlts 40(4/39(k)±2n MSVOO 39A00) K/Ca±211 an AnalysIs (10.) )%,,)

3091610 HLP-98-400328399 W199186d 04084 0.0316 I 23 00.10 0.19 91.34 0.145 30.080 M010r191 wt44 , P1.10.0 07.75% 07,77% L00000n Omgon 609,1.1 Ens,*0.10 2.78 0101000811 ,.Oo A.raIVSl b5 A08IlIioolEnon 00,10 1.0000 ErronM.grO80.5.n

P101.ot Jord,, 70181F25t66 0,3392 00.0811 192 00,25 6 0.124 00.072 1,526060, 0SU2095 .23 52% 223.92% J-ool.. 0301675 60101,46 ElnOro 0.25 Sffir..do,d AnetyOnot 6081.025

283.AGE 000 I so' HLP-9$-40 wr 2B3-99 Jordan I

Ar-Ages in Ma

WeIghted P18(086 1,2320,10 Tote) Fosion 1,026025 Normal(500(1015 1.20±012 )nverse50001011 1.21 oO.12

MSWD 079

91-

aL

CUnll.Iedne 3M6 Released (16)

2B3.AGE so' HLP-98-40 WI 2B3-95 'so Jo.dan

0.0040 Ar-Ages In Ma

Werghted P)9t660 0.0039 1,23 0,10 Total Foss, 1.02 * 025 Noons,)1500010, 0.0034 1,2060.12 (110.018Is000Ion 1,2160,12 03028 MSWD 0,76

00623

0.00(7

0.0 0,4 0.8 7.2 I 6 2,0 2.4 2,8 3.3 39Ar I 40k 213

HLP-98-42

IflCrem.ntal 36Aro37Ax(±ui 38Apop39Asp 4) 39A1)k) K/Ca±2* No)

000214 600C 1 001307 0.93610 0.00884 0,90494 0,46439 1.48 aO.22 10.71 3276 0.439 90.034 000215 700C V 0,00843 227610 0.00702 0.01041 0.40046 1.54 20.26 15.53 31.24 0.172 20.013 660216 600C 1 5,30417 2,73183 0.00306 0.54326 0.22169 1,23 80.51 15.23 18.84 0,088 *0,007 000217 900 C 1 000261 1.94350 0,90199 0,23576 010060 129 01,49 1148 8,08 0052 00.004 000218 1050C 000123 080107 0,00160 0,09494 000600 000 *0,00 000 3.26 0047 00006 000219 1266C 0.00040 0.57130 0.00058 0,04639 0,00006 0.008000 0.00 1.59 0.035 90.011 005220 14006 0.00175 8.55842 0,00016 0.12289 003771 094 06.94 6.80 4,22 0.008 *0,001

0.03172 1587841 0,02327 2,91480 128121

Information ± On Analysis R.aufts 4O)r1J39)±2* Age2* 39A2(k) K/Ca±29 )M.) MSYSO (%n)

S8IrWI IILP98-42WrZB2-99 o4834 80.0522 147 00.16 040 9083 M014631 ,4.,60k 66.8629 *10.79% 01081% 0.07300008 1.0201109 012809 Eotom.l Error 80.16 3.18 9860400911,6119 4001001 58 58096.101 o,ror*0.18 1.0000 En60M.g,4598800

Proleot 0981. 1808 F00188 0,4366001130 134 90.34 7 lnaotaliofl 0052609 Ag. *25.71% 8 25.71% 0,079 *0.003 0.001691 6088*81 Error*0,34 Standard 28,04 An0190oot Ens,o 9,34

2B2.AGEso' HLP-98-42 Wv 2B2-99 >0' Jordan

AE-Ag56mM.

Weghtod Plateau 1.47±0.16 Total Fooron 1.34*0.34 Normal lSOChron 1.37±077 Inverse loocirron 1.39 ± 0,74

MSWSI 0.40

CS6IUI46O.3flAr R.taaaad (%)

2B2.AOE 9>, HLP-g$-42 WV 2B2-ti$ 9>' Jordan

0,0045 Ar-Ages inMe

Woightnd Plataao 0. 0039 1.47 ± 0.16 Total Fusion 1.34 ± 0.34 Normal lSochron 0.0034 1.37 ± 0,77 Inverse Isochnor 1.39 ± 0.74 0. 0038 960960 0.55

0,0023

0. 2017

2.0 0.3 0.7 1.0 1 4 1.7 2.1 2,4 2.8 SCAr l40A8 214

HLP-98-54

Age ±2x1 34() 355,(5)394k) 4OArll) 4007) 35) K/Ca ±201

0551003 50CC 0.01137 0.43093 0,30720 0,55235 2,04994 11,33 *0.55 37.85 10.74 0.544 ±0.073 0551004 7000 1 0.00993 3.23022 0.30553 1.25219 4.60693 10.80 *0.36 60.98 25.13 0.172 ±0.032 OOCI005 SOOt 1 0,30213 301300 0.00109 1.14155 3.57942 1037 ±0.19 5585 22.20 0.153 *0.020 0551005 SOOt / 0.30153 2.45009 0.30244 0.02923 3,18790 10.41 9 0.17 50,60 18.07 0,160*0.019 0551007 bOOt 1 0.00155 1.91855 0,30474 0,42513 1,42400 l023 ±0.31 7551 0.27 0.995 ±0.012 0001008 1100 t 0.00298 1 1.30540 0,30630 027915 0,02509 10.13 *0,56 5121 5.48 0,006±0.011 0001009 1200 t 1 0.01311 4.13191 0.01196 0.35721 1.26355 10.51 *0,59 24,80 8.95 0,037 *0.054 0001010 1400t 0.01315 1 5,55857 5.55351 5,15584 5,55097 11,02 55,55 13.34 3.22 0.012 50.037

005505 22,57327 0,04395 5,14248 1791932

Infennatlon Age 3SAr(k) Ranolts 40))/39k± 25 ±201 K/Ca ±201 on Analysis Me) MSWO)

041151± .98-54 nrO±ralrn±U )5..fldan) 21 W45ghNd ±0.0402 8928 M.sIe1lte 1042 00,18 1,81 o.sea oo.o34 9$-98 ,±55 056.52 51.41% 01.52% 7 LOc±90fl 0055±0 External ErrOl 00,16 2,45 S1e6.OoeIT 181)0 60±14*1 09 428119±1±8.15000.15 1.3939 ErrOl 18±089±89±11 p0±I J±150fl ±0.0598 7±481P0818± 1054 00,22 8 o.oge± 1118980±11 03112495 Ar ±200% 0207% 0,015 .1.08188 0,001597 EeMlr±I Error ±0,22 018*4915 2804 5*8114031 Error±0,21

F1.AOE >5, HLP.9$-54grcs9ndn.ass(B.Jorrdan)2F1-9 5>2 Jordan

Ar-AgeshiMa

748401164 P188800 10.42±0.16 1*181 F*xtorr 10,84 ± 0,22 Normal lsochron 10,38±0,15 In*8150 I500lv±n 10,37 00.15

MSWD 1,51

0 *0 20 30 40 50 85 70 50 90 150

C9n.±88t15± 39Ar ReIe.s.d(30)

F1.AOE >5' HLP-98-S4grcundn.ass(B.Jordan)2F1-99 5., Jordan

0.0045 Ar-AgeshiMa

WoIghted P191890 00039 10,4200.16 7±188 Fonor, 10,840 0,22 55005881±0*199.1 0,0034 10,3600.15 11150156180*800.1 10.370018

5,0025 1857)0 1,75

0.0323

0,0017

2.00 005 010 015 0,19 0,24 0.29 034 0,39 39Ar/4OAr 215

HLP-98-59

Incremental H..tIng 38Ar(o)37Moot38A1(ol) 39A1(k) Ag.±218 40A1(!) 39A&lk) 40k(r) K/Ca±218 (K.) (%) 000306 6000 0.00360 0.72751 006014 016078 080397 750C 0.00204 0481.4 ±714.9 7.01 9.71 0.040 .0.004 / 0,00138 5.54200 0.00000 0.50167 0.03128 050398 1562 .232.4 7.11 35.38 0.040 00.004 9500 / 0.08072 5.53803 0.06060 0.54568 000309 10500 0.02503 1359 .246,5 10.88 33.17 0.042 .0.004 / 0,00070 2.51801 000050 0.20233 980450 12500 0.00426 61.2 .032.7 2.01 02.30 0.035 .0.003 0.00093 3.05249 0.00016 0.88608 0.05408 000401 1637.1 .23022 1541 5.64 0.011.0.002 14500 0.00038 10.02793 0.00000 005652 0.109495426.0.7383.7 49.33 3.58 0.003 .0.001

3 0.0077429.30546 0.00002 0,84509 0,30679

Into,matlon Age±218 on Analysis RSSUft* 40(r)/39(io)±2o NS)M) K/Ca±20 (K.) (%,n)

S.11ç4. HLP-98-59 WA 268-99 M,t.n.1 W.lghl.d 00476 0,0555 1358 .161.1 8083 w56., P849.06 11608% 0,045 oO.006 t0009011 .116.08% 3 Orsoon 60190101 4.30 60118.1 Enor 9161,1 S199090&71±0, 54 An55llooI Eon, .161.1 0.0000 EOn! MotjflhIloo000

P490.1 JoolOn 108.4 P99409 15919.508 o.osss 00.1127 5415 .321.3 0052689 Ag. 060,44% .06.44% 6 0.024 0,001 J-v&u. 0,00168 £0191801ErrOr .327.3 StOfldOnJ 20.04 An&tSs6 Error 0327.3

2B8.AOE'3>HLP4$-59 WR 2B899'9>Jordan

3000 Ar-Age. In Xi

Weighted P1.1,85 135.80160.0 2500 Total Fosion 541.5± 327.3 Nonnba) (soChrofl 063,5±478.0 floors, )sOchrofl 2000 103.30432.7

MSWD 005 1500

1000

1±69056*.115.

000 C- 0 10 20 30 40 50 60 70 80 90 000 COfllgtetIfle3M, R&.a,ad (%)

2B$.AGE"9NIP-il-SI WR 281-lI2'>Jordan

0,0565 Ar-Ages In Xi

Woightad P56,80 00039 138.8±061.1 75594 P50401 541.6±327.3 0,0034 Nonflel(5005,08 163,5±418.0 5405r,n 182.3 ± 432.7 0,0028 MSWD 0,10 00023 '\

00017

0 3 7 00 14 17 21 24 28 39A, I 40A, 216

HLP-98-66

4OArl) 36A055) 37A0(oo) 38k(4) 39Ar(K) 4OAr(r) A59±20 K/C4 ±205

000480 COOt 1 0,00050 017058 000106 001769 058011 340 0535 1188 1.04 0040 00,002 900405 700 t 1 0.00020 055109 000067 006550 0.00330 2.05 01.58 40.50 0.27 0.043 00.002 060402 SOOt / 0.00050 2.05601 0.00045 0.00130 0.26664 2.72 00,32 02.10 17,76 0.063 00.002 980463 SOOt / 0.00030 4.00476 0.00012 0.80170 0.47726 2.44 *0.18 67.80 35.48 0.080 00.002 900404 ¶000 t / 0.00017 2.64716 0,00023 0.39070 0.00335 2,61 00.26 55.57 20.45 0.062 40,002 550450 1155t / 0.30021 1,35672 0,00053 0.13211 0.11407 2,67 00.80 64.76 7.75 0.043 *0.002 960480 1200t / 0.55030 1,99375 0,00009 0,09577 0,06077 2,80 41.24 47,46 5.05 0.038 40.001 050487 5400 t 0.00137 458101 0.00457 0.11124 0,56546 4.57*1.20 20,60 0.59 0.010 *0.000

E 0.05325 56,54262 0,00003 1.89806 .00204

I.foomilien Age ±255 On&s.ty.Is R.SU6O 40(,V39(kl ± 2* MSYSD 3r) K/Ca ±2*

040W'. HLP-98.80WR 504-98 0,6265 50744 58.9085 51,01.5001, 254 0,58 0.047 00,007 L408000 05850., E05.1fl81000040,13 2.45 55808504111854 Ano55sI 0,01o5081 0180100.53 5.5506 0,so.69o4So,5os

d4n 55808 0% 0,541.500 0505000 TOSOIFO4500000 2.72 0 0.04300,005 Jv&o. 0.001754 1,155,595 Ens. 55.15 558049,0 26.04 O,8ls404lEno * 0.16

6E4.AOE 050 HLP-Be.0 I WR5E4-6$sos Jordan I

Ar-Ageshi Ma

WolgiStOd P590.90 2.54 00.13 Total F04500 2.7200.18 No,n85 10005,50 2,4550.10 Inverse Isodrr.fl 2.5000.17

MS/sO 0,50

5 10 20 30 40 50 60 10 00 90 100 CUntOlattSS 39A, R&.aand(00)

6E4AOE so' HLP-9g-68WR5E4-96 000Jordan

Ar-Ag..in Ma

WilgIlted P595890 0.0039 2.5480.13 T.tei Fools. 2,72 50,16 Non,sal 0005,05 0,0634 2.4350.56 lnOnrs. 50010105 2.000057

00028 MS/K) 049

00023

00017

0,0 02 0,4 0.6 0,0 1.0 1,2 14 1.6 3CArl4OAr j 3M,140A, Ag (U.) if:; " SIw SI0 I.5 I0 P I.5 ii V V !!!!!!!!! ! a 8 a III 000000 en . Iiq: 4 ;; q 4 V 218

JR-91-21 (MacLean)

Ago ±211 4%(r) 3902/k) 36Ar/o/3lAIio*) 3802(45 390.r(k) 4002ir K/Ca ±20

000104 90070 0,00467 0.57724 0,50348 0.89455 5,55552 2,97 *0,13 40,90 10.64 0.698 *0.051 000197 70070 1 0,00105 0.10230 0.00150 1.41854 1,23112 2.41 *0.12 75,98 17.10 0.868 *0.068 000184 50070 1 0,00136 1.28633 0.00312 2.82606 2.24730 2.36 *0.09 84,74 31.92 0.878*0.066 000166 90070 1 0,00094 1.13068 0.55423 1.79421 1,00156 2,33 *0.17 6425 21.74 0.682 *0.051 000100 100070 / 0,00107 0.92249 0.00777 0.77015 0,58170 2.10 *0.46 04,79 9.33 0.366*0.027 000101 110070 / oxen 030361 0.00346 017721 0.10600 1,55 *2,60 55.91 215 0028 *0047 000102 120070 1 0.00167 2,293470.01133 0.3*060 0.23007 1.93 *1.63 32.72 4.19 0.060*0.066 000193 130070 / 0.30267 1,95251 0.01501 0.23570 0.13275 1.83 *2.06 3,54 2.74 0.000 *0.000 000164 140070 0,xeao 000000 05 000000 o.00en 16,71 *000 3.00 000 0000 *0000

L 0,01423 9.19804008002 820178 696767

Infolmatlon Ago± 39A7b0) Renolto 40(r9l30/k)±2* 2* MS/ND K/Co ±20 OilAIISIYS*S (MO)

SaorØ. Jordan) 2013-01 Jfl-91-21WI/B WsEgtrSd 06546 *0.0235 237*0.07 00,16 0.078 00.004 M8l*r*0 *1101. look 01.18.0 *2.75% *284% 7 L00000n 01800n 0,01*0*1 Elm.±0.07 2.45 SI*b.08*l1l±0* MaIy*I 0 01*1108*1 ErrOr*0.07 1.0000 011*1M.81400a90fl

P10i001 Jordan TotaIFoSoo 0,9400 00,8406 236 *0,14 0 o.xe *0.015 I1V*O 0002959 *99 *5.64% *5.80% 0.001541 External0,101 *0.14 St.ncterd 28.04 401*1100*1011*1*0.14

0340JR-91-21 wr (B. Jordan) 2893-91 0010Jordan

Ar-Ag.o In Ma

Weighted P00400* 2,37±0.07 Total F*eioo 4.0 2.350014 04,15*18011*1*11 242±0 13 floors. lsochr*fl 2420013

3.0 MSWD 0,49

2.0

0.01 III) 0 IS 20 30 40 50 60 70 60 90 100 C9660196I693M1 Relea06d (%)

00C18&AOE23*1JR-91-2lwr(B.Jordan)3B13-99 015* Jordan

0,0045 Ar-Age. In Ma

Woightod P1±0.00 0,0039 2.37±0.07 101*1 FoniOrl 2.36±0.04 Nonrord(50*01011 00034 2.420 0.13 Inverse53*01109 24200.13 0,0020 MSWD 040

0.0023

0,0017

0,0011

o

0.0000 0,0 02 04 08 08 7.0 12 1,4 0,6 3IArI4OAr